The way kRO has designed it, players are to do Eden Group quests from 12 - 140(?) and then do instances the rest of the way as there are no world maps with monsters that are level 150+ (aside from guild dungeons).
For the 100-160 range, there's Abyss Lake, Odin's Shrine, Thor's Volcano, Biolabs, New World, El Dicastes dailies, Mora dailies, and Malaya. (Keep in mind the dailies are mainly good for getting gears, not so much EXP.) In terms of instances, we have Fenrir & Sarah, Airship Assault, Old Glast Heim, Geffen Magic Tournament, Cursed Knight, Devil's Tower, Faceworm Nest, Bakonawa, and Sara's Memories.
iRO customizations include Xellie's Gramps TIs, which range from 70-150 and whatever's left of my Bounty Boards project, which should help you get to max level.
Your mileage may vary.