This is a 3.5 km climb (moderately hard, if your acclimatized, painful if not) to the park entrance, then a 9.5 km fast downhill on a dirt road; lots of fun. There are awesome views of mountain peaks between the clouds to the north, and if you go very early in the morning (and you should, the crater fill with clouds as the morning progresses), great views of the creater bottom to the north east. When you get to the bottom of the crater, head east (see my other Pululahua trail description for the one west) into the main crater. There is a decent biking road that cuts across the middle, follow it straight (or ride around the crater as well, there are other roads) until you get to the opposite (east) side, where there is a very steep zig zag up the crater lip. This climb is excrutiating (I was able to ride about 85% on a FS bike, fully acclimatized), but much shorter than riding the road out (the climb here is about 2 km max). When you get to the lip, ride down the paved road from the viewpoint until you get to a dirt road on your right, follow that along the edge of the ridge to meet up with the climb on the main road to the ocean; from there it's a gruelling 3 km or so up to the crest, then down to the Texaco station where you left your vehicle, and where they sell drinks!
Drive north from Quito towards Mitad del Mundo, then past it another few miles. You will pass a signposted entrance to the Pululahua Park, don't take this one, keep going to the top of the hill (on the main highway to the ocean), then about 1 mile past the top of the hill is a Texaco station. You can leave your vehicle there. Another 200 Meters down the road to the right is a sandy road heading straight up towards the ridge to your north, ride up this. There is a house (concrete) immediately south of the sandy road, don't take the earlier one that has no construction near it. I think there may be a sign too.