Which city (or cities) would you consider to be Europe's best kept secret?

Question

Answer

Here's the less-touristy places I can recommend:

Galway (Ireland)
Bratislava (Slovak Republic)
Chester, and Brighton (England - north and south)
Aix-en Provence (France)
Heidelberg (Germany)
Piran (Slovenia)

Answer

I don't  think in a city, I think in a country, and is Russia  the country's best kept secrets, everything there is a mystery

Answer

Chernobyl - Ukraine
Pripyat - Ukraine

They were polluted during the Chernobyl Atomic Plant Accident in 1986.
But they are still usefull for extremal tourism ;)