Iliniza Norte is a classic climb just outside of Quito. At just over 5000m it is a great mountain to test your altitude skills and the great trail lower down makes for excellent high altitude trail/sky running. The ridge trail and final cruxy pieces involve some class III-IV scrambling and can be very dry or very snowy, so make sure you have experience and check on conditions before you head over. Most climbers go up the ridge and loop down the scree field, though you can go up/down either side. This is the classic "lollipop" loop though, starting in Chaupi main square.