In the belly of a whale

Related:
* Biogrowth

Usually a whale is involved, hence the name. But this is not limited to whales or their stomachs. Commonly these are very unrealistic depictions of the internals.

This does not include mechanical creatures (robots and such) in general because they may be indistinguishable from artificial structures like space stations, but they may be included regardless if the experience is less so. For example, one may see the Citadel Station SHODAN was in control of in System Shock as her body, this case is very similar to being inside the body of other robotic entities and is very different from what one would experience inside an organic creature. The space station however is still largely indistinguishable from regular space station and thus does not qualify here.

One of the oldest examples of this fantastic story setting can be found in Book of Jonah, of the Hebrew Bible, where Jonah is swallowed by a great sea creature, commonly assumed to be a whale, and spends three days in its belly after which he's vomited out.