Best Mario & Luigi: Bowser's Inside Story Bowser Locations

What are the best areas inside of Bowser in Mario & Luigi: Bowser's Inside Story? Let's find out. I'll only count the major areas with actual levels inside of them. So with that being said here is the list.
The Top Ten
1 Flab Zone

The Flab Zone is, visually, perhaps the least attractive of the areas, at least on the DS original. However, in my opinion, it's still the most fun and interesting area visited. It's the third area you explore while Bowser is in Bowser's Castle. His brainwashed minions force him to eat a bunch of cake, causing him to gain weight. Mario & Luigi must then travel to the Flab Zone, the area where Bowser stores all his fat, to find a way to make him burn off those calories. Overall, it's a somewhat creepy experience, but in a really good way! Since we're playing this inside Bowser's Castle, the music is an "inside Bowser" remix of the castle's song, which adds to the experience as it sounds kind of distorted. It easily makes it the best of the five major areas visited inside Bowser.

2 Airway

Now, this area certainly has some atmosphere and climax, as it's the last area visited inside Bowser, near the end of the game. Bowser has defeated Icelord Midbus, but the Dark Star has escaped to inside Bowser and is stealing his DNA to become even more powerful. It's Mario & Luigi's job to chase it down. Bowser can also breathe in the icy breath coming from Midbus' corpse, allowing the inside of Bowser to freeze. This enables Mario & Luigi to traverse on ice, similar to the Luiginary Sun in Dream Team. Plus, the music! It's a remix of the Deep Castle music in Peach's Castle and is an even better version of the already classic song. Overall, it's another amazing area!

3 Pump Works

The second major Bowser area of the game is set on Plack Beach, right after Bowser has defeated the Blooper statue boss. Bowser can then drink the water shooting out of it, filling his body with water. This helps the Mario Bros. traverse areas inside the Pump Works. I don't particularly remember much from this area since it's one of the first, but it was pretty fun with the gimmick. Overall, it's a great area.

4 Trash Pit

The Trash Pit is the absolute first area of the game, not just inside Bowser but the first overall. Right after Mario & Luigi are sucked into Bowser's body, they end up in the Trash Pit and must find their way out. It's not a huge location but big enough to make it onto the list. Here, you find hammers and other Toads that got sucked up as well. There's not much else to say about it. The music is a remix of the Underground Tunnel theme, which makes the area feel a bit empty and bland, but it's not a significant issue.

5 Energy Hold

The Energy Hold is pretty frustrating. After the amazing level that was the Flab Zone, our next area falls short, offering less than half the fun. It also features the same remix of the Underground Tunnel as the Trash Pit, making it even more bland and boring. The level is essentially a quest to collect all the keys needed to progress to the main area. The gimmick is also quite frustrating: Bowser can move in front of a light to make certain blocks appear and disappear within the level, and it's a chore to switch between them. Therefore, it's easily the worst area of the game.