Nestled into a strip of Barnum Park running along the north side of the Sixth Avenue highway is the Trestle Bike Skills Course — a series of bumps, berms and jumps made just for bicycles. BMX, mountain-bike and downhill cyclists of all abilities are welcome on this circuit, with man-made dirt hills and wooden ridges created to challenge both first-timers and experienced risk-takers. Maintained by the city and dedicated volunteers, this specialty bike course is like no other in the nation — plus it's part of the Parks and Recreation system, so it's free to use. A treat for both riders and onlookers, the Trestle Bike Skills Course entertains drivers along the congested freeway and allows high-flying cyclists to get air while exercising.