Weidman's Tunnel??

I have searched every nook and cranny and some how I got 2 stairs that take me back to level 2 I missing something or am I a
Just stupid? Help???

It is a tunnel, not a cave, and so you have to make your way back up levels. Just take the stairs to level 2 that you DIDNT come through and continue. Just think about it as a tunnel, like below.

Level 1------------------------------Level 1
----------Level 2----------Level 2
--------------------Level 3

Yep, Thats the way it Goes