The Abandoned Sewers (aka Catacombs) is a forgotten place under Rathleton. Left to crumble away, fearsome creatures started to rule it.
The combination of Demons and Grim Reapers make this place very good in terms of both Loot and Experience, specially for Paladins because they can use Holy Damage spells, but also for other vocations and team hunts.
There is a chance that you'll find a Slime Slide on the south-west part of the dungeon depending on the votes cast in the Rathleton Quest. You can also use the small room south-east of the Slime Slide as a safe place if you need.