One of the top recurring themes in shmup visual designs is building levels or whole games around flying in someone/something's intestines and blowing up the baddies there. From what I've played, the following ones are most memorable:
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X-Multiply. I do not know what the hell Irem were smoking to send our hero into the guts of an infected woman to destroy the virus that spawns micro-eyeballs within the body. It's totally outrageous
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Lifeforce. I consider its rebranding a nice idea, actually, for several reasons. If Salamander was brought to US intact, there'd be one awesome game. But now there're two

And without all that meat on the first level it won't be so memorable
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Abadox. Thank God I didn't have it on my NES back in the day, or I'd shit my pants.

A planet with the giant mouth inhabited by H.R. Giger's kitchen experiments...
- Not a game, not even a level, but the first midboss in
GG Aleste. That's one of the few things I DON'T want to see in HD

In an alternate universal, Soldier Blade II has already been crafted by Hudson Soft and Compile with proper tate this time around (c) PC Engine Fan X!
Sega tried and failed. Nintendo didn't even try. (c) Specineff