Neat levels!
I can tell why it's a Koopa Kavern, though I have to admit, the turtles are one of my least favorite enemies in the game. But that's not your fault.
This is a nice set of levels. I liked the way you used the textures and lighting to create a vibrant aesthetic, though, as mentioned before, some rooms do tend to get too dark. The levels do border on cramped, but not anything nearly as bad as we used to get. Back when the editor was jankier, it was a lot easier to think you're creating a massive chamber and end up with a skinny weenie hallway. This zone is right on the boundary between too-cramped and ok, which I think is fine if you're deliberately trying to slow down the player.
The levels look nice, as I said, but a lot of the sectors were too square. I think perfectly-rectangular platforms are okay, but perfectly-rectangular rooms, especially a lot of them stuck together, gives the player the feeling that he's in a Minecraft base rather than an SRB2 level. If you made the boundaries of the rooms a little less straight and a little more organic and uneven, I think you'd improve the aesthetics by a fair margin.
I really liked how you paid attention to the nooks and crannies of the level. It feels evenly-decorated, and there's a good amount of ring monitors, emblems, and extra lives crammed into the easily-overlooked corners of the level. On my second playthrough, I took the time to slow down and look around, and I felt well-rewarded for my efforts. This is what good explorability is :)
And what's this, a good third act? Again?? The last level I reviewed, Quiet South Island, also made clever use of the Egg Slimer boss. Yours made even MORE clever use of him! The wide arena and turrets really made this boss a lot more exiting than usual, and for that you deserve applause. You guys keep showing me that Egg Slimer is a lot more versatile than he first appears.
Good work, and I hope I see more levels of yours in the future!