This is level 4 of the Memory Evaluation.
Note: Since you can only use the Gentleman in this tunnel, he will be the only recommended character.
In this level, the first portion's path tells you the path you need to take in the second half of the level. Fortunately, the path in this level is not that hard to memorize, so you should be able to beat this without much difficulty.
First, take a right turn, then turn left diagonally. Note that you can reduce the risk of falling by doing a jump and land on the left hand side. After that, do a large jump and land on the right hand side again. Walk diagonally to the left and you will have already beaten the first half of the level.
As for the second half, repeat the process. The orange gate marks the end of this level, and the start of the next one.