(towns, caves, camps, tombs, mines, ruines, forts, farms etc.) ...someone any idea?

http://www.uesp.net/wiki/Skyrim:Places

Is there a number out?

Iirc, there are 343 unique "fast-travel" locations in vanilla Skyrim.

Add in all the interiors houses, castles, and stuff just not marked on a map....plus extra-dimensonal places like Pelagius's mind, inside Azuras star....

plus all the Dawnguard locations, Dragonborn locations, and 3 houses for Hearthfire?

A lot more than 343. Just a rough estimate, I would say close to 700-800.

Remember in Fallout3 and NV, there was a Perk that would light up every possible location on your map?

I wish there was something like that in Skyrim...

Because even after many, many hours and plenty of foot-travel, I'm still finding new things I've never encountered before.

Just to be safe, 1000 in Skyrim and Solstheim.

Is Whiterun 1 place, or 3?

Is each cities "district" 1 place, or a 3rd of a place?

I guess the number could be whatever by how you define it.

Plenty to see though, that is for certain.

343 (?), well OK (only Skyrim without Addons), but with 700-800 (with Addons) you are joking, are not you?

Do you mean locations with map markers or every place of interest? As for the map marker one's I have around 400 discovered locations iirc...i'll check when I can

if we are counting House Interiors as their own locations, as well as various Cells in each Dungeon, as well as places like Palagius's mind, Sovengard, or Sanguines realm. not to mention all the unmarked areas of interest in the Wilderness, I would say above 1000 Easy (with DLC).

Way too many to count.