Slovakia
This is one of 24 "Tajchy": a unesco heritage preserved artificial water reservoirs made in 18th century for mining purposes. Now used for recreacional purposes (swimming). I highly advise to pay some of them a visit, you can find some campspots (and freecamp too) along some of them. Perfect for cycling around in the hills.
More info on Tajchy:
https://en.wikipedia.org/wiki/Tajchy
Good resources on Tajchy, cycling routes and accommodation:
http://www.bajkomktajchom.sk/index/language/en
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This is one of 24 "Tajchy": a unesco heritage preserved artificial water reservoirs made in 18th century for mining purposes. Now used for recreacional purposes (swimming). I highly advise to pay some of them a visit, you can find some campspots (and freecamp too) along some of them.
More info on Tajchy:
https://en.wikipedia.org/wiki/Tajchy