El Teide is not only Tenerife's highest mountain but also is an icon and a visitor magnet. Even an Irish childhood without much in the way of international travel did little to deny me a passing knowledge of the name since it featured in a souvenir that an acquaintance brought to us. It just shows that sunshine holidays to the Canary Islands were as prevalent then as they are now.
It is possible to get most of the way to the top using a cable car though you need a permit in order to continue to the top unless you stay overnight in Refugio de Altavista and do your ascent before 06:00. Altitude is in excess of 3500 metres above sea level even for the top cable car station and the summit is at 3707 metres so this is not an outing for the blithely indifferent. There even are days when the cable car does not run because of the weather conditions so they are not always as benevolent as seen in the above photo.
The combination of weather and altitude make reaching the top of El Teide a serious mountain excursion and it also is a fragile if harsh environment. That is enough reason for there to be a permits system and altitude sickness is an issue too so this is an outing that needs planning. For the ascent and descent, it might be that hiring a guide is hardly an excessive action.