One of my favourite stadiums I've been to is actually Bristol Manor Farm.
Only because it was an absolute dump!
Sloping pitch, falling down advertising boards and terraces, a massive drop to the pitch one side of the ground, fences falling down around the ground, barbed wire around the first aid cabin and a train line a few steps from the dug out. The worst kept ground I have ever visited which included a septic tank next to the food kiosk, but looking around at the fans and their passion etc I actually enjoyed the visit overall