Just to say that just because Downing has laid it all out on a webpage, doesn't mean their facilities are better than other Colleges. I had a flip through and they seem pretty standard. Consider where your department is (West Cambridge?) and Colleges that might be near that. For example, if you are going to be in West Cambridge, then the more modern Colleges, albeit built before accessibility was properly considered, may be much more accessible eg Churchill, Fitz, Murray Edwards, Robinson etc.