Where can you Find an isolated House for Rent?

In the UK, or findaproperty Fotocasa. In France and Spain Seloger enalquilar.com. You really need to get an idea of where you want to be and then look in that area, rather than random search websites.

Consider this

Note that an isolated rural property may not have the basic amenities you expect in a common property. It costs a lot of money to bring power lines and gas pipelines to serve an isolated property. In addition, you may have trouble getting broadband or cable TV if you are really far from civilization