depending on your gear/class at lv.40 ~50 if you have nice gear Cruma is the best. but if you dont have good gear.
places better then Ivory tower
Alligator island
forest of mirrors (here you have a mirror mob which drops some spell books and the mirror spawns more mirrors so if you can kill them fast it is pretty nice exp)
sea of spores (could get some nice sb drops for Adena)
Timak Outpost
then at higher levels try either these
Cemetery
outlaw forest
enchanted valley
field of massacre
Patriots
Forbidden path
in principle Field of massacre you can still there up to lv. 74 or so if you want to there alot of peole but alot of mobs and spawns only the group mobs can be tricky but just make sure you have some HP pots and make sure you take the Quest in Aden from the warehouse dwarf for the card trick, you have a very low chance if getting 200kk.
the quest item drops from mobs in Cementry, forest of mirrors, blazing swap, Field of massacre, seal of shillen and few other places