Hévíz in detail
Hungarian Tourist Agency (https://hellohungary.com/en) Not ground-breaking but the best single website on Hungary.
Tourinform (http://tourinform.hu) Good for visitor-centre locations and general information.
Lonely Planet (www.lonelyplanet.com/hungary) Destination information, hotel bookings, traveller forum and more.
Hungary Museums (http://www.museum.hu) A list of every museum in the country currently open to the public.