In reply to Palmaciu66:
Google Tenerife route 040 - yes it's possible, there's a nice video, and there are FKTs around 6 or 7 hours return trip. You are not allowed to go to the summit without a pass, in theory, but I don't know how they can stop you outside the 9 - 5 times that the guard is present.
Not done it from the sea myself, it is on the list, but I'm not sure how easy the navigation during the early stages would be in the dark, through the banana groves. Just under 60km for the return trip, and nearly 4,000m ascent (0 - 4 - 0 is the cute description).
If you are not used to the altitude you might struggle a bit...