Mount Teide is located in a national park and the highest mountain in Spain. There is a gondola from the park to the top, but you can only book tickets online and it is recommended to check if it is running in the morning, as it often does not run when there are high winds. The trip up to the park is scenic, with great views to the ocean throughout. In the park itself there are a lot of volcanic features which can be explored on well marked trails. Ps: there are more visitors than the picture suggests, visit early.