TROLL PARTY FTW!!!!
Abyss...well. Abyss is a place with same identical monsters as you face every single day. Some may be stronger, some weaker. But one thing they all have in common is that they drop an item called Abyss Gem. Abyss Gem can be randomly gambled for an item, at the warehouse keeper. Such items include chitin, high class weapons, chitinshell (if you're very lucky), and my favorite...bezour and rice cakes

. Im not sure whether level in abyss makes a difference, coz I hardly spend any of my time there, its a waste. But many people got rich of abyss, so i wouldn't complain. Oh you can also be killed by a player, but you don't lose any gold/exp/NP; however this rule does not apply when you are killed by a monster there (you still lose 5% EXP).
Hope that helped.