It is worth mentioning that the volcano's crater is considered a restricted area and requires a special permit to get there. The request is sent through the official website, which is free of charge. It is advisable to take care of getting the permit in advance (a month or two, depending on the season).
There is only one hotel in the park, "Parador", where you can stay, but only for one night. By the way, when you rent a room, you automatically get a pass to visit the crater - this is another way to obtain permission to enter the territory of the volcano's crater.
Here is also operating one of the world's largest observatories. It is open to the public, where everyone can watch the night sky.
Buss tours with excursions to Teide's National Park are held from any city on the island. However, you can easily reach it on your own by rented car.
http://www.volcanoteide.com