I'm onto my third base. The first was a makeshift home that just gradually expanded. The second was a good strong base in the plains with plenty of options for farming and lox and great connections to some black forest with thistles and blueberries. Then I found a lovely little coastal place with a tiny little section of meadows for building, bordered by a decent bit of forest, with plains and a mountain just over a relatively small river. I planted some pine trees and used some iron supports to start a big bridge / walkway from my base over to the point where the plains / mountains join. Nice route for frost glands, mosquitos, fulings etc. without them ever spawning close enough to hurt my lovely new base, but with the walkway on the other side of the moat that I'd dug.
Then, in real life (the worse of the two lives if you ask me) I went to cook a meal without logging out. I checked back once to see which base I was at (I was in the new one) and if I was alive, because I often get mosquitos stuck in the plains base somehow. Everything was hunky dunky. Until I came back after I'd finished cooking and looked outside. Some event has happened, I'm not sure which, but my base on the good side of the moat is fine and the river walkway is just a pile of wood on the floor / river, with the supporting pine trees nowhere to be seen.
Some 'orrible cunt has come along and chopped my trees down, which has caused the entire walkway to fall over. If I could sue Surtlings or Trolls or whatever did this shit, I would.
TL;DR – don't just fuck off in real life to do things and assume everything will be fine when you come back.
Source: https://www.reddit.com/r/valheim/comments/mov4xo/ive_learned_a_lesson_i_should_have_already_learned/