Room 18 - The Spider King's Hoard!!1!one
This is it! This is what you braved the mysterious well for, the uncountable riches! But... a small box sits behind the door in this room, no bigger than an outhouse. You cautiously test the lid and it opens freely, revealing two big handfulls of coins dating back to rulers decades ago, and a half-dozen gems. You appraise the find as worth about 80 gold coins total, which should at least pay for a decent healer once you see daylight and a good party at the inn.
Time to pack up all the loot and retrace your steps... you did make a map, didn't you?
Leave the King's chamber, heading south