From where the road breaks off from the main road to Nono, there is a 500 M climb that can leave you breathless, but it then it hits a road that goes along the slope of the mountain (the north side of Pichincha). Take this road to the right, and follow it for several km (it's basically flat). After some time of going in and out of the ridges, you'll get to a deep cut into the mtn where you have a bit of a rocky climb to a gate and the first camping area (you will have been seeing the town of Nono below you just before this). Go through that first area, up the hill (easy climb) around a couple more ridges until you get to the park entrance. Pay the fee ($5 for foreigners) and then follow the road as it continues to skirt the egdes of Pichincha. The road eventually narrows to a path, and just keep on it as it goes through 4 pedestrian tunnels that cut through ridges (long enough to be almost pitch black; you can ride them by just letting your bar ends, if you have them, grind along the tunnel wall. Watch for deep gouges if you lose your balance though...). The path winds inwards towards the north slope of Guagua Pichincha, and some non-spectacular waterfalls, and some other edifice. When you get there, hike around, or head back out the same way. This route is mostly flat, with a few doable climbs, even for someone not really acclimatized.
Drive north along Avenida Occidental from town, past San Carlos and Atucucho, and then on the slope down after that is the road to Nono on your left. Follow the road towards Nono for about 9 km (cobblestones) until near the crest, just before it starts to go down, you'll see a road off to your left, signed, to Hacienda Yanococha. You can ride to this point from the highway if you like, but the cobblestones are a pain, and it's best to get a pickup at Cotocollao (the market) or a cab from town; it's worth the money.