There are no loot chests in the ruins, only unidentified Fire Arrows from the Kobold Commandos, and the spell scrolls from Lendarn. But that includes Cloudkill.
The compass orientation of the exits in the Ruins is opposite to their alignment above ground in Gullykin. North exit leads to Jenkal's house, next to Jenkal, if he is still alive. North of Jenkal's house is the Winery and Temple, and inside that building is where the stairs from the south Ruins exit lead.
There are only two side quests which can be completed.
- Getting armor from the Undead Knight in the region of 1450, 360 to 1130, 490. You can then either take it to the Ghost Knights at 730, 985, for 1500XP, or use it to trade for The Vampire's Revenge, a sword that damages its user and heals the target.
- Killing the Ogre Mage who has been directing the Kobolds to attack Gullykin, and the evil mage Lendarn who is just up the hall. Also in this area are 3 Ogrillons, 2 Kobolds, and up to 5 Kobold Commandos from the respawn point further up the hall.
There are also, and only, two things standing in the way of those objectives, other than Lendarn & co. themselves: Traps, and respawning Kobold Commandos shooting Fire Arrows.
Monsters in Baldur's Gate cannot respawn if the player or companions have the respawn point in line of sight. This can be used to the player's advantage.
When the party gets to one of the 'R' respawn points on the map above, park a character there until the party reaches the next one, and so on.
The Undead Knight is hostile, but gives a speech before attacking; the Ancient Armor weighs 15 lbs.