Obviously, some people must WANT to do this - see Port Lympne, London, Whipsnade, etc. But I've never understood why!
It used to be keeper accommodation. I doubt Bristol has much of that left now.
It seems all these overnight setups are very expensive. It would be nice if a zoological park could set up a standard hotel, with a view over a field exhibit. Why not outsource it to a reasonably priced national chain hotel, such as Days Inn here in the states or Premier Inn across the pond? They would pay all construction and operating costs, no expense to the zoo, and the zoo gets a percentage once they are up and running.
...it can get VERY cold. They even highlight this in the joining instructions. Not sure why the couple in the Porsche only came in shorts without a jacket.