1. Approach the pit. Hug the "down" wall (the wall that separates you from the entrance)
2. As you walk along this wall, you're actually on a ledge, above the slimes
3. Continue walking left to the back corner. You don't actually need to, but that's my favorite spot.
I blew up the map on uoguide and circled the gray tiles that form the ledge.
Can't post a screenshot for you at the moment, but I will if you still can't find it.