Parc des Buttes-Chaumont is the nicest place in Paris IMO - an old quarry turned into a park; with rocks, a lake, caves(!), waterfalls, etc. A charming, peaceful, interesting and all in all a great place...

There's a similar place in Kielce - the Kadzielnia Reserve. Smaller and, unfortunately, much neglected. However, with some creativity and a lot of cash it could be turned into a fantastic park...

Anyway, I had no idea that in Cracow there are similar places. One day, totally by chance, I went to the Twardowski's Rocks park and the surrounding forest (where, by the way, there are several quite interesting caves). I was really surprised when I saw that the forest opens up into the quarry in Zakrzowek. A splendid place, and in the middle of the city at that! But go there on a sunny day - the water takes on a beautiful turquoise color.

Not far away, you can find rocks that also were part of the quarry. Pretty high, quite interesting, and in the dry part of the park. :) From their top you can enjoy a great panoramic view of the whole city.