I found these structures underneath the roof of an old wooden bird house that hang for years on a wall covered by ivy (Hedera helix). The last two pictures were taken two weeks later, after a dry period.
My first thought was, that this is some sort of fungus, but on closer inspection they seem to be hollow tubes made out of silky material. So now I'm thinking these may be insect cocoons instead. But further than that I have no idea who could have made these. I would be happy about any suggestions!