as noted, august can be hot in most parts of europe so depends on your tolerance. however in my view august can be a good time to visit European cities such as Paris as the locals are on hol and there are good rates at business hotels (getting a cool, relaxing hotel in an optimum location to minimise walking is a must). two ryanair destinations ex GRO you might want to consider are venice and alghero. Venice itself will be hot and slightly smelly but a fantastic experience nonetheless. treviso itself is nice and you could also hire a car and drive into the S Tirol (german speaking part of Italy) for great mountains, interesting ambience and - I think - one of Europe's most interesting experiences viewing the iceman (perfectly preserved in a glacier from X000 years ago) in Bolzano. Alghero is on Sardinia which is the quintessential, and not yet ruined, mediterranean island with Italian cuisine to boot.

A driving alternative would be over the border into france - the valley up from perpignan to vernet les bains and the pyrenees is delightful.