You'll see the 2 half-pipes there. Not really large. In summer, people will sometimes bring a small jump ramp. Excellent junk-food joints nearby. When the weather is good, you'll find skaters at night too.
Asphalt is variable.
Sometimes it's extremely bad, sometimes excellent. In summer nice 2 relax after some heavy-duty skating. From Central Train Station, take tram 1,2,5,11 or 17 to leidseplein. At leidseplein, ask some innocent bystander the way to vondelpark.