The red with blue dot trail runs from North Ridge Road near the Ice Skating Rink to Irwin Run where Babcock Blvd intersects Pierce Mill Rd. The trail was originally constructed in the mid 1990's By Dave Brunger and Bill Kirk as the Rainbow Trail. This runs from the Skating Rink side to the Wisconsin Shelter. This section of the trail climbs and descends with technical features, lots of rocks and twisty singletrack.
The trail was then extended in the 2000's by Trail Pittsburgh as the Pfundstein Trail, which runs from the Wisconsin Shelter to Irwin Run. Pfundstein was named after a German mountain biker who worked in Pittsbugrh and loved riding North Park. He unfortunately died of cancer and his family donated funds to build the Pfundstein trail. It is marked with a plaque on a large stone along the trail adjacent to the Wisconsin Shelter. Pfundstein is a faster flowy downhill trail.
The trail was built to be ridden from the Ice Skating Rink side to the Irwin Run side, but it can be ridden in either direction. The climbs become descents and the descents become climbs in the opposite direction making things more interesting! The climb from Irwin Run along Pfundstein is a hard one and this can be bypassed by taking the Red Bridle Trail
up to the Wisconsin Shelter from Irwin Run to ride Rainbow backwards.
To find the trailhead from the Ice Skating rink side, start at the Olympia Shelter parking lot (across Pierce Mill Rd from the Skating Rink). Ride up North Ridge Rd for ~50 yards. The trail will start on your right. The trail winds up the initial ~.25 mile climb before beginning the long flowing ride. The trail is continually marked with red-blue blazes, but does not cross any other trails which makes it easy to unplug and cruise through. Their are multiple opt-out locations in case you get tired or run short on time. All opt outs put you on North Ridge Drive, which you can take northward and end up back at the double lot. You can cross the road at the Wisconsin Shelter and take the Red Bridle Trail
down to Irwin Run which is a fun, fast, steep and more direct downhill route.
More information on North Park Trails and Freeride area at Trail Pittsburgh's website: