I wish to know what the the most isolated building in the world is, with "most isolated" being defined as "the longest distance to the closest building". Building complexes count as multiple buildings. A building is defined as any permanent man made structure that is used either for habitation or human activities. So this includes houses, office buildings, fixed rocket launch sites, military bases embedded into mountains,... Essentially everything apart from walls and other fortifications, small outdoor sheds not meant for living or working like outhouses or storage sheds and wells. For example: the Svalbard seed vault is considered a building, BUT it lies a couple hundred meters from the Svalbard airport, so it's not the most isolated building in the world.
Clarifying the comments: (Ant)Arctic research stations count as multiple buildings if they're modular like Halley VI. If they're 1 contiguous building, they're counted as 1 building. Tents don't count as permanent. I don't know enough about igloos to know how permanent they are, but let's say they don't count. Seldom inhabited radio stations count.
My own research has pointed towards the lighthouse on a remote island off the coast of Cornwall to be a likely contender, since it's 70 kilometers away from the nearest building.