The largest natural rock bridge in Europe, Pravčická Brána is the symbol of the beautiful countryside known as Czech Switzerland, which sits on the border with Germany. It's a bit of a hike from Prague, but if you plan ahead, it's the perfect day trip. Take the train to Děčín, which takes just over 90 minutes, followed by the local bus to Hřensko, the nearest village, which takes another 30 or so minutes. The driver, or the tourists getting off, will let you know
where the best stop is for the bridge. From there, it's a lovely and atmospheric walk up through the forest to reach the rock formation, which comes complete with a museum and restaurant called The Falcon's Nest—supplies are brought in via pulley. This being the Czech Republic, there's also a pub where you can order fine beer in the shadow of the bridge itself. For 75 Kč, you can scramble around nearby rock formations, which have a similarly alien appeal, for a better vantage point. A series of gentle, well-marked hikes on pretty forest trails and mossy gorges will take you a circular route back, ending up in Hřensko. The highlight of these trails is being punted along the river—when the paths run out—in a precarious boat with a ferryman who tells you (in German and Czech and hand gestures) how the rocks over your head look like different animals and monsters. Each boat trip costs around 50 Kč.
If you want to see a bit of real Czech magic, head for Pravčická Brána. It's a schlep from Prague, but it can be done in a day if you plan ahead.