Sometimes, in the rush to see the "major" sights, really nifty things are overlooked. Additions to the list are welcome. Diatribes against the pencil museum are not.
Minack Theater, Cornwall, UK
Pencil Museum, Keswick, UK
Notre Dame de Chartres, Chartres, France
Guggenheim Museum, Bilbao, Spain
Sewer Museum and Tours, Paris, France
National Museum of Prehistory, Les Eyzies-de-Tayac, France
A week on a self-drive narrowboat anywhere in the Midlands of England
A week on a self-drive cruiser though the Great Glen/
Caledonian Canal in Scotland.Perigueux, France; and Penzance, England
Hiking the Hadrian's Wall trail coast to coast and getting lost trying to follow the Offa's Dyke path in Wales.
Lands End, UK; Cape Finisterre, Spain; Cape St Vincent, Portugal
Alignments at Carnac, France