A few kilometres south of El Teide peak, across from the Parador Nacional, lies this geological freak show of twisted lava pinnacles, christened with names such as Finger of God and the Cathedral. The display is a consequence of various processes: old volcanic dykes eroding or solidified vertical streams of magma. The most bizarre overture is the Roque Cinchado, while to the west spread out the otherworldly bald plains of the Llano de Ucanca.
Note that the Roque Cinchado is eroding faster at the base than above, and one of these days it is destined to topple over (so maybe don't get too close!). It is such an iconic symbol in Spain that for years it featured on the old 1000 peseta note.
It's also the most popular spot in the park and viewed by nearly 90% of visitors, so the car park is perennially jammed (you may have to drive around to find somewhere to park); most people just leave their cars or tour buses for a 15-minute obligatory glance.
The 1½-hour trail that circles the rocks is still pretty well travelled, but there are some excellent, photogenic views and it's a terrific hike, with quite a steep section at the end.
