From the World Heritage inscription:
Situated on the island of Tenerife, Teide National Park features the Teide-Pico Viejo stratovolcano that, at 3,718 m, is the highest peak on Spanish soil. Rising 7,500 m above the ocean floor, it is regarded as the world’s third-tallest volcanic structure and stands in a spectacular environment. The visual impact of the site is all the greater due to atmospheric conditions that create constantly changing textures and tones in the landscape and a ‘sea of clouds’ that forms a visually impressive backdrop to the mountain. Teide is of global importance in providing evidence of the geological processes that underpin the evolution of oceanic islands.
Mount Teide is the highest point in all of Spain and it sits at the center of Tiede National Park. The park itself is a giant caldera with geologically recent lava flows and a desert like environment. On the drive up to the park you will pass through several different ecological zones including a forest of Canary Island Pine Trees. Tiede really is one of the most spectacular parts of the Canary Islands and if you are there on a clear day you will be able to see at least four other islands.
View my complete list of UNESCO World Heritage sites.