On the summit of Mařenka there is a freely accessible lookout tower where you can spend the night. The best place is probably in the shelter at the bottom (concrete floor), another option is under the stairs (but it may leak) and the viewing platform at the top is protected against rain. But it's windy as hell there and the lookout makes scary noises in the wind. There are tables, benches and a fire pit nearby.
According to the map, there are many wells in the hillside, but I haven't checked.
Whenever...
The lookout tower is located on the blue hiking trail.