I am at Level 23. For the past 3 levels, I have noticed that caves, dungeons, etc. seem to be getting smaller. Some, like the Red Belly cave are cleared in 3 minutes. Is this just coincidence that I am running into small areas, or do the dungeons, etc. get smaller with higher levels? Seems strange. Lower levels took a long time to clear out.

That is a cave not an actual Dungeon.dungeons takes like 30-1 hour.

You can go in any dungeon you want in Skyrim when you are level 1. It's just coincidence you come accros this smaller ones now

There's no dungeon that changes it's size during play, so I'd have to say you just hit a stretch of smaller dungeons. If you're doing radient quests, they're more likely to send you to a small one since they tend to avoid intersecting the main/faction quests, which have larger ones.

Probably it is just that you are getting fatter.

At least Dwemer ruins are HUGE. A few times in there, they are even so huge it gets boring and frustrating and I just want them to end already.

I feel the same way. Everytime I hear those machines as I enter a Dwemer ruin, I hit save and know I am in for a long night.

Agreed,some of them drived me mad,had alot of ways to go and and taked like 3 hours to finish it.

Yeah, its just a coincidence.