If you want a real nice run in a beech forest get on the C (red) metroline and go south. Get off at "Roztyly". It takes about 12 minutes from the Muzeum station. There are only two exits, get out through the right and 25 meters away you see the woods. Walk straight up to the trees where the path starts. There are some signs marking different trails. I followed the yellow trail, according to the signs 6,5 kilometers long, but it turned out to be about 9 kilometers. Partly hilly. Mostly wide with gravel surface. There are several paths going criss-cross in the forest but just keep to the yellow one and you will see, after approximately 9 kilometers, some signs nailed to a tree, on the back of the tree there is a sign ("Metro 1 km") pointing right, downhill. If you go the whole path you will basically have made a big circle around the forest. You will meet quite a few walkers, bicycles and families, at least during the weekends. After approximately 7 kilometers there is a restaurant at your right, which can come in handy if you feel dehydrated and urgently need a beer...
Run the Planet - Prague