With the river providing the ever-present temptation to jump in the water (not in the Wisła!), this riverside pool complex comes as a relief. The most centrally-located swimming place in Warsaw, you'll find it right next to Lunapark on the river in Saska Kępa. Thanks to the ridiculous name, the locals call it 'Spartan,' and spartan it is - an old communist era sports facility consisting of two Olympic-sized swimming pools, very basic shower and changing facilities. One of the pools has a pretty sweet slide and lifeguards are on duty to stop the kids from running (and drowning, we suppose); there's also a small beach area for adults to lounge around while the kids make sandcastles, and like we said, the food and drinks of Lunapark are right next door. When it's hot and you need to just get wet, what more could you want?
Free parking is available nearby. To get there by public transport, take trams 7, 9, 22, 24 & 25 from the city centre (Centrum) to Rondo Waszyngtona next to PGE National Stadium, from where you can either walk through the charming Saska Kępa area (taking a turn right at ul. Zwycięzców), or immediately switch to bus 138 which will take you to the front gate 5 mins away at stop Krynicza. You can take the same 138 bus to/from the city centre around Plac Unii Lubelskiej/Plac Na Rozdrożu near Łazienki Park.