So my father's mid-life "I should buy a boat" moment was "I should buy a 100-year-old barn with no water and a leaking roof on an island and convert it into something habitable".
This was 10 years ago, since then I've spent a month or two every summer (and some very cold winter weeks) helping him make this a reality. The first few years it was mostly me and him who spent time there (my mother was... less enthusiastic about the project), sleeping in tents and washing dishes in lake water while rebuilding the roof and cleaning out the place. There were three generations' worth of rubbish in there, and next to the house an old rusty boat with a wooden deck supported by sawed-off telephone poles built around it. We also ended up building a small cabin next to the barn to have somewhere more comfortable to stay during construction.
Four years ago we finished the bedrooms, the next year with some help we finished the bathrooms and the kitchen, and after that the third floor. Last year we converted the cabin into a sauna. Over time, as the place has become more and more habitable, even my mother and siblings has started to appreciate the place, and friends and family have started to come there for extended stays. Last year I think we were around 7-8 people staying there in July. Hence all the bread-baking! :)