Just beyond Prague's south-western edge, the landscape changes abruptly. The city's apartment blocks give way to wooded hills and limestone cliffs, and the Berounka river winds through a valley lined with summer cottages, villages and the occasional factory. You start and finish on the plateau above the valley, near Třebotov and Černošice, a pleasant, practical place to start and finish rides without fighting through the centre of the capital.
This is the edge of the Bohemian Karst, an area of limestone hills, caves and gorges that stretches west towards Karlštejn. The rock has been quarried for centuries, and some of the old quarries, now flooded and overgrown, are surprisingly beautiful; the most famous, nicknamed Velká Amerika, has sheer walls dropping to a turquoise lake and is sometimes called the Czech Grand Canyon. Karlštejn Castle, built by Emperor Charles IV in the fourteenth century to protect the crown jewels, stands on a hill above the Berounka a short ride away.
The rides that start here head far to the north-east, to the Krkonoše and the Orlické Mountains near the Polish border, so the first part of the day is about covering distance. The Prague ring road will take you around the city, but on weekdays it clogs easily. The local roads in the Berounka valley are narrow and winding, with tight bends, railway crossings and cyclists, and they make a pleasant warm-up or cool-down at either end of the day.
There are fuel stations in the surrounding villages and on the main roads towards Prague, and pubs and restaurants in Černošice and the other valley towns. Czech pubs are a fine place to end a ride, with cheap, hearty food and excellent beer, though remember that the legal blood alcohol limit for riding is zero. On summer weekends, the valley fills with Praguers heading to their cottages and to the river, so traffic can be slow. Early mornings, with mist rising from the river, are the most atmospheric time to ride.