Crash Bandicoot 2: Cortex Strikes Back/Hangin' Out

Another level set in the sewers. However, this one is a little different from the ones you have already faced. After an initial phase in which you have to go through a conduit, eliminating enemies that come towards you at high speed, sections in which you have to proceed hanging from the bars and parts in which you have to proceed in a tube avoiding indestructible diamond-like robots alternate. Naturally, there are more robots here and they move faster. Towards the end there are also some pools with the electric eel. The crystal is easy to spot and can be found towards the end of the path. A little further on is also the detonator to blow up all the Nitro boxes.

The bonus area is right after where the crystal is and is quite tricky. You have to perform a couple of long jumps to avoid dangerous Nitro boxes and then you have to destroy some bouncing boxes suspended in the air, being careful not to fall.

In this level is one of the hidden portals that leads to the secret Warp Room. To find it, after taking the crystal, instead of proceeding, walk towards the screen. You will find a hole in the floor that leads to a secret area. This area is downright treacherous, although you can collect some extra lives. In fact, you have to proceed holding on to the bars, avoiding robots that move very quickly. You will have to move with the utmost timing. Fortunately, these robots are at a lower height than those you've already encountered, so you can use Crash's ability to pull himself up and grab the bars even with his legs, to avoid them. At the bottom you will come to a seemingly dead-end room. Follow the line of wumpa fruit to teleport. You will then be able to access the secret level Totally Fly.

Getting the gem
The only available gem is obtained by breaking all the boxes and shouldn't create any particular problems for you. Just be careful in the bonus area. There are no boxes in the secret area, so you don't need to access it to get the gem.