One of the most popular cycling destinations for a short, intensive after-work ride in Slovenian capital is certainly Toško Čelo. In the afternoon you can see all sorts of people and bicycles, climbing the hill.
Interesting part starts from the Bike Park Ljubljana, very nice place if you are trying to kill yourself in a funny way or at least trying to broke a shoulder.
After about 3km of climbing and about 100-150m of difference in altitude, you will be awarded with a great view and effortless downhill ride.
If your bike is suitable for downhill/off road you can take some of steep dirt paths. Otherwise, with a road bike you will enjoy very smooth tarmac.
Additionally, you can enjoy riding on the cycle/pedestrian path that is passing through the wood.
If you are in Ljubljana, and you want to sweat a bit or avoid becoming fat after eating a lot of bograch - try this challenge.