The best way to prgress if you cannot find your own way is to move with the zerg....or wait for one if it hasn't formed yet.
There are 3 chambers in level 1, 2 in level 2 and 4 in level 3 plus the final instance boss fight near the key chest at the very top.
3 chambers are active at any one time and open and close randomly.
Each section/level can be locked by a boss fight or event. So if you run across an event, good chance you are going to be required to clear it to continue forward.