Relax in a park

Kampa

An island between the Vltava River and Čertovka, a side channel of the river, where you can see a huge mill wheel that belongs to the 15th-century former Grand Priory Mill, this is one of the most romantic and picturesque places in the city. The grassy areas of the island are widely used for picnics and relaxation.
Kampa, Prague 1, http://boat-trips.cz 

Letná Park

This vast park provides not only a pleasant place to sit and relax, but also unparalleled views of the city, especially from Hanavský Pavilion - a unique cast-iron building with a restaurant.
Letenské sady, Prague 7

Stromovka Park

Stromovka, being the largest park in Prague, has a lot to offer. The park itself has perfect flat and wide paths for biking, rollerblading, skateboarding, and running with many grassy fields and ponds ideal for picnics, frisbee, and grilling . The paths lead to Prague Zoo and Troja Chateau, a walkable distance away on the other side of the river. Further bikes paths from Stromovka lead you along the river to places like Divoká Šárka, a nature reserve with some good hiking and outdoor swimming options. There are several food and beer garden options in and around the park, so you can stay there the whole if you so desire. Also, towards the entrance of the park near the tram stop, “Vystaviště Holešovice” you can find the historic exhibition hall Vystaviště, a planetarium, fairgrounds with a fair in full swing in the spring and summer, an indoor swimming pool, and the Tesla Arena with hockey games and concerts.

Petřín Hill

Here you can visit the particularly magical locations of the Rose Garden, or rosarium, at the top of Petrin Hill, Kinsky Garden, and the Seminary Garden with its more than 2,100 fruit trees. The Carpathian wooden Church of the Archangel Michael is a local architectural rarity.
Petřínské sady, Prague 1

Franciscan Garden

A unique natural oasis in the city centre.
Jungmannovo náměstí, Prague 1

Shooter's Island

An old-time atmosphere and exceptional views of the city directly from the surface of the Vltava River.
Střelecká ostrov, Prague 1