Bought the most beautiful Victorian bay-windowed stone house. It had wet rot, dry rot, woodworm, rising damp, falling damp (is that a thing? It was WET everywhere) and had had (literally) nothing done to it since the 1970s, apart from a new roof in the early 1990s. However, I stood three paces into this monstrosity on the first viewing and knew I'd live there forever.
We took it back to stone - removed everything that wasn't a supporting wall (and some that were), dried the fabric of the building out, treated the wood, replacing where treatment wasn't suitable, and then started rebuilding. We knocked down the existing kitchen extension it had no fucking foundations and discovered the entire thing was built on sand. We shelved plans for a second storey extension, and bifold doors, and spent the money on concrete and rebar for the foundations of the new kitchen/diner extension (they are suitable for having a second storey, when we get the money to do it!).
We obviously did a full rewire, a full overhaul of the heating system, insulated properly, replaced the guttering (which was a mishmash of original cast iron, 1950s and 1970s, none of which met properly), tanked the cellar, replaced all the windows.
We got the house for 20% less than it was on the market for (against a full market offer from a developer, because we said we wanted to live here and raise DC here, and it was a probate sale), and spent the same again refurbishing and fitting out.
Would I do it again? Fuck no, I'd buy the house up the road that someone else had spent a year arguing with builders over. We used an all-in-one firm and he subcontracted the bits he couldn't do (tanking the cellar etc).
I do love my house though, and I was so glad we could stay in our rented flat while this one was being done up. There is NO WAY we could have done it while living here.