I just got there at level 15 with my ice wizard . I did every quest in wizard city except for sunken city. I also did not do crab alley. My myth wizard got there at level 12 and my fire at level 13. I would do all the quests in wizard city before krok because it makes everything sooooo much easier.
i started around 11-12 with my Fire & Balance, that was after i beat Fowl Gaze (dont mind bad grammer) or NightShade
~ Blaze SoulHunter Level 32 Fire School
For me, Merle gave me the Foulgaze quest at level 11. I tried and failed the my first run, So I got some friends who had the quest, we succeeded, so we went back to Merle and he told us to Nightshade. What I'm saying here is that you have to fight both Foulgaze, AND Nightshade.
I was level 15 when I got into Krokotopia. I made sure I finished all of the quests in Wizard City. (I always finish side-quests). My other wizard (life) was level 15 as well. Ashley Deathflame, Balance, Level 60
I started around my Journeyman levels in Krokotopia. I guess I got into Krokotopia when I was like Level 16. BTW I was balance school. OH I still wasnt a member at level 12 so that's why. I became a member at level 12 so I directly couldn't beat the 3 streets when I was a n00b.