In addition to some nice coastal scenery, you can find some great pacifist run treasures in a sea cave, complete some interesting encounters and one easy nonviolent quest, and also find a quest further south that will automatically transport you to Nashkel when it concludes for a reward of 1000 xp, making this our preferred route to reach Nashkel before continuing the investigation of the mines.
The Sword Coast & The Shipwreck (one map east of High Hedge)
This is the furthest northern coastal map you can reach, since sheer cliffs cut it off from Candlekeep, and the other seaside areas are inside Cloakwood and Baldur's Gate (neither of which you can reach until later chapters).
If you run into a nereid named Shoal in the central northern part of the map, she will try to deliver a cursed kiss that will kill any player who receives it. After a skirmish (which she'll give up on shortly), it turns out she is being held captive and obliged to do this by "Ogre-Droth," after which she'd raise the ally she killed and try to get you to kill him to release her. To do this, you'd have to rely on a compromise like charming other creatures in the area to dispatch Ogre Droth, in which case you could free Shoal for a reward. (But you won't need to do this if you don't want to get involved.)
Mad Arcand and the Shipwreck
Heading west to where the rocky cliffs meet the sea (southwest of where Shoal is, if you encountered her), you will find a riddling gnome named Mad Arcand.
Fortunately, he'll like you, and ask you to bring his his cursed "Ring of Folly" from a nearby shipwreck. You'll find the shipwreck just a short distance southwest at the edge of the sea, and can take the ring. (Don't put the ring on, however, as it's cursed.)
When you give the cursed Ring of Folly back to Mad Arcand, he'll thank you and give you an "Oil of Fiery Burning" and 300 xp.
Note there is a huge "Carrion Crawler" that will chase you on this strand unless you're using stealth, and might pen you into a narrow area if you're not careful— but as usual the Baldur's Gate monsters aren't any threat to NPCs outside your own band, so you don't have to worry about Mad Arcand getting attacked by it.
The Brother of Davaeorn
You can meet a character known as "The Surgeon" in the lower part of this map, who will tell you that he is the brother of a powerful mage named Davaeorn, who has long since turned to evil and killed many, including their own father. He'll give you a Potion of Magic Protection in the event you should ever confront Davaeorn yourself.
The Sea Cave & Abandoned Lighthouse
This stretch of the Sword Coast is the site where a an old abandoned lighthouse stands over a cove with a few small sandy beaches. This stretch of coast is an excellent place to visit on a pacifist run because of the sea cave on the north side of the cove, described in detail below.
There is also someone you can recruit here, if you're looking for another thief: A young woman named Safana, who you can find on the western side in the center of the map. Safana will pretend to be in awe of your male party members in order to try to persuade you to protect her on a quest to raid pirate treasures from a dangerous cave at the cove.
Not far from Safana, there is also an astrologer you can talk to a little ways north, and a gypsy aways south who will offer to read your palm for some gold, but will then become upset by what she sees and won't want to tell you anymore.
The Old Lighthouse
If you traveled all the way southwest to the lighthouse, you'd find a woman named Ardrouine who says her son went exploring the lighthouse ruin, but has now been surrounded by worgs that gathered at the base of the light house, so that he won't come down. We tried to solve this, but unfortunately found that even after we lead all worgs far from the lighthouse, charmed them, and also tested rendering them unconscious with Sleep and Color Spray spells, the son still won't seem to come out of the lighthouse no matter how little danger remains. (So there's probably no way to complete this quest without causing deaths.)
The Cove & The Sea Cave
The sea cave you can find on this map is full of useful pacifist run treasures, but the cave is guarded by fairly dangerous Sirines. You can reach the cave by going to the central western part of the map, where you'll find a large sandy beach, though you'll have to use stealth or other tactics to get past some hobgoblin bandits and archers lurking in the area.
You'll then be able to follow the cove on the north side until you reach another sandy beach, above which you can travel north a ways to reach the mouth of the sea cave containing a hoard of pirate treasure.
However, you'll also be threatened by Sirines south of the cave:
Probably the best way to get past the Sirines is to use stealth or invisibility to sneak past them, so that their leader, Sil, never sees you: If you succeed, then Sil won't open the dialogue to tell you that it is "not your place" here (after which she summons more sirines to attack you).
The main reason the sirines are dangerous is because they can cast Dire Charm and cause your own characters to be out of your control while the spell lasts, as well as becoming a danger to your own allies. (Sil and the sirines also cast a higher-level invisibility spell on themselves, but that won't be a problem for a pacifist challenger with no intention to attack them in the first place.)
By this time (after visiting High Hedge) we always had the invisibility spell for the mage/enchanters, and decent stealth skills for the rogue/thief characters, so sneaking past them the first time allowed us to get inside the sea cave without being seen.
Inside the cave, you'll find many passages leading in various directions, and discover that the caves are guarded by at least two flesh golems (as well as lots of harmless bats fluttering in the caverns that won't attack). You can circle around the caves in several directions, but the paths are narrow, so it's much better to avoid being seen by using stealth, if possible.
The treasure hoard is in a large stone jutting from a pool on the northwestern side of the cave. One of the flesh golems sometimes lumbers up here, but by waiting awhile, we found that he'd just leave and stomp back down toward the south caves after a short time.
The hoard of pirate treasure:
In order to grab the treasure, you'll need someone to break out of invisibility, assuming you used stealth to get inside the cave. (A rogue/thief that can then re-conceal themselves without wasting an invisibility spell might be best, and you can pass the treasures to your allies without breaking their invisibility status.)
The hoard of pirate treasure contains over 300 gold pieces, some valuable potions, some darts, and three excellent pacifist run treasures:
One is a Wand of Paralyzation that will freeze enemies in place without harming them, and in many cases works better than the similarly useful Wand of Sleep, including against key boss-like NPCs you'll encounter later.
The second is the "Cloak of the Wolf," which will allow the wearer to transform into a wolf for a period of time, and consequently move as quickly as one, which might be helpful to escape some situations.
The third is a "Manual of Bodily Health," which will give you a permanent +1 to the Constitution of whoever reads it, though it can only be used once. (This is still very good, since in Baldur's Gate your attribute scores typically stay the same after character generation, rather than giving you more attribute points to allocate at level-ups.)
The Flesh Golems in the sea cave seemed to be immune to spells like Sleep and Color Spray, so when you're ready to escape, it would be ideal to re-cast invisibility on anyone who isn't hidden in shadows. This would also help to avoid letting Sil see you outside the cave, and summon the other sirines to attack you for setting foot on their beach. (We did this with a mage who had run out of invisibility castings and almost got killed, but managed to resist the Charm spell and still managed to get away from the Sirines even after Sil attacked us.)
When you're ready to leave this section of the coast, you can reach the final map along the coast by traveling to the south.
The Ancient Excavations & Commander Brage
(third map down the sword coast, south of the lighthouse)
After traveling south of the map with the sea cave and old lighthouse, you'll reach a remote area with some rocky crags of banded rock and lots of pine forests. Stealth is ideal here, because this area is heavily populated with Gnolls, wild beasts, Tasloi, and a hobgoblin bandit (and will later fill with even more dangerous foes, depending on your choices if you visit the Excavations).
There are paths between two bands of forest on the western side of the map, and below that (where a dirt road turns further inland), there is a hobgoblin bandit to watch out for named Ba'Ruk. Ba'Ruk may not seem to be very smart, but if you let him speak and demand you give him all your gold, he'll summon a large band of Kobold Commandos who fire dangerous flaming arrows that can easily slay 1-2 pacifist run characters with low HP in seconds. (If you avoid Ba'Ruk, though, the kobolds and their fire arrows probably never appear.)
The Ancient Excavations & Charleston Nib
If you head east toward the upper-central part of the map, you will find a site where a large group of diggers are unearthing an ancient stone settlement from beneath the cliffsides.
They are led by an archeologist named Charleston Nib, who will tell you that they could use more protection due to night-raids by enemies in the wild surrounding area. If you agree to help Nib, you'll soon also be approached by a treacherous partner of Nib's named Gallor, who will propose that you kill Nib and split proceeds from any treasures discovered. We turned Gallor's offer down, and shortly after that Nib announced that his men were on the verge of penetrating into the main interior chambers of the ruin being unearthed...
You'll then be taken inside the ruins automatically, into some cave-like old chambers where a disturbing stone idol of an evil god named Kozah will be found. At this point (with no way to avert it that we know of) Nib's diggers will become taken over by the extant powers of evil emanating from the idol, and will start to attack you in force.
The good news is that the diggers won't harm Nib at all, but there doesn't seem to be any way to bring this entire scenario to conclusion by removing the curse without being forced to slay the otherwise-innocent diggers that have been bewitched.
However, you can steal the idol of Koza (stone idol) and take it with you, then give the diggers the slip and run away without killing anyone.
As soon as you leave the ruins with the idol, a dark undead entity called a "Doomsayer" will confront you and seem to be indicating in an ancient language that it wants the idol, but there didn't seem to be a way to make it dispel the curse by giving the idol back to it, so the only remaining option seemed to be to run away.
(The only use we know of for the idol itself, by the way, is to combine it with some other things at the Ruins of Ulcaster in order to receive a vampiric sword from Ulcaster's ghost. The stone idol is otherwise only worth a small amount of gold.)
Commander Brage & The Journey to Nashkel
Whether or not you are being chased by the bewitched diggers and hostile Doomsayer from the Excavations (which you could choose to skip), you will find the remains of a grisly scene southeast of the Excavations, in a large dirt clearing.
On the way there, you'll likely meet a cousin of Commander Brage's named Laryssa, who will tell you to stay away from Brage, as he has gone berserk and slain many, including his own family.
Unfortunately there is no way we know of to revive any of the dead family members or others who have been slain, but it turns out that Brage has actually been bewitched by a cursed sword, and there is a way you can put a stop to further evils by talking to him above the scene of carnage:
Brage will tell you a macabre riddle (to which the answer is "Death"), and when you solve the riddle, he will temporarily be restored to sanity, and ask you to take him to the Temple of Helm to face execution for his crimes, which he never wanted to commit.
If you agree to this, you'll automatically be transported all the way to the Temple of Helm in Nashkel immediately (regardless of how many enemies from elsewhere on the map might be actively chasing and attacking you), and the priest of Helm there will remove the cursed sword. The priest will also persuade the grief-stricken Brage that his life still has purpose by serving Helm to atone for his crimes, since it was never his own will to commit any of the atrocities.
As for your role in ending the evils: You'll be awarded with 1000 gold and 1000 xp, as well as increased reputation and a strength potion, along with the cursed sword that caused all these evils to begin with.