It is just 8 km from us to Hrádek n. Nisou (nice bike ride btw.) where you can bath, swim and relax in a lake called "Kristyna".
And of course there are many open air pools in Liberec.
During wrong wheather you can visit - All year long you can use the Liberec Swimming pool or Aquapark Babylon Liberec - slides, whirlpools, tobogans, sauna, water attractions, wild river, massage, etc.
You can have a fun here also on bowling, XD Cinema, Laser game, Amusement Park, IQ Park etc...