Do I have to visit every biome variation to earn the "Adventuring Time" advancement?
This blog states that there are 36 biomes in total that need to be visited to obtain this achievement:
Forests
Birch forest, birch forest hills, cold taiga, cold taiga hills, forest, forest hills, jungle, jungle edge, jungle hills, mega taiga, mega taiga hills, roofed forest, swamp land, taiga and taiga hills
Colder biomes
Cold beach, frozen river, ice mountains and ice plains.
Warmer biomes
Beach, desert, desert hills, mesa, mesa plateau, mesa plateau F, savanna, savanna plateau and stone beach.
Water biomes
Deep ocean, ocean and river.
Other
Extreme hills, extreme hills +, mushroom island, mushroomislandshore and plains.
The good news is that a lot of these biomes are pretty interconnected anyway, so the list isn't quite so daunting.