Getting the Blue Key (13)

You'll start off in a pipe. Just exit it, and you'll see two booths right in front of you. The booth on the left has a Pig Cop chilling inside – take him out and then head in to grab a Shotgun. The booth on the right has a Large Medikit. Both booths have a switch that'll disable the forcefield around the revolving doors nearby. Pick one of the revolving doors and head through.

After passing through the revolving door, you'll immediately have to fight two Pig Cops that drop down from above. Keep following the path, and you'll reach what's called the Babeland Hub. This is your central point for the level, connecting to all the other areas. To your left, you'll spot a Pig Cop hiding behind some boxes. Across a pool of water, there's a grate where two Captains are waiting. To your right, a window holds two more Pig Cops. If you check the top of the boxes to your left, you'll find Shotgun Shells, and behind them, a Large Medikit. You can climb those boxes to reach a ledge with some Pipebombs. Don't forget to look behind a Duke sign for some Pistol Ammo.

Now, about the fountains: they've got Octabrains and Slimer Eggs lurking in them. It's tricky to hit them with Pipebombs because the fountains are pretty big. Once you've cleared them out, grab the two Microwave Expander Ammo rounds on the ground. There's also a grate here that leads into the D-Cup Ride's pool.

The only area you can access right away is the D-Cup Ride, which is easy to spot thanks to a sign on the wall. In the hall leading to the ride, there's a booth containing Steroids and two Pistol Ammo pickups. Go through the revolving door, and a Captain will attack you. As you approach the ride itself, two Mounted Guns will open fire from the opposite side, and two Troopers will be positioned on a ledge above. On the ride platform itself, you'll find two Captains. The ride has two cups that spin around a central pole. You can get to the areas on the other side by riding these D-Cups. You need to reach all three cups and hit the switches on each small platform. You'll find Chaingun Cannon Ammo on the right platform and a Chaingun Cannon on the center one. Doing this will lower a part of the ride's central shaft, revealing the Blue Key you're after!