Why the volcano comes first
The climb is the longest drive of the three and the one most exposed to weather, so it goes first. If cloud, wind or dust ruins the view, there is still a spare day to try again; put it last and there is not. It is also the day that asks least of you physically — you sit for two thousand metres of altitude and someone else takes the bends — which is why it pairs well with a travel day or a late arrival the night before.
The floor, not the summit
What the tour shows you is Las Cañadas: a caldera sixteen by eleven kilometres with its floor at about two thousand metres and walls standing five hundred metres above the road. That floor is where the photographs come from — the eroded monoliths at Roques de García, the pine at Pino Gordo on the way up, the black and ochre pumice of the caldera plain. The cone above it is 3 715 m by the IGN and Grafcan survey; the 3 718 on the signs and in the UNESCO listing is a trigonometric figure from 1920 that nobody has bothered to repaint.
What the lift does and does not do
The cable car runs from 2 356 m to 3 555 m, costs €42 return for an adult and is a separate purchase from every tour on this day. Last boarding is 17:40 in summer and 16:00 in winter, and strong wind closes it without notice — no tour refunds the day for it. From the top station you are still 160 m below the crater. That last stretch needs its own permit, €15, with a timed slot booked through Tenerife ON weeks ahead, and no tour can include it. Plan the day around the floor; treat the lift as a bonus and the summit as a separate project.
If the air is grey
Saharan dust — calima — covers the island on roughly forty per cent of days, and in calima Teide is seen worse from the caldera than from the beach. Check the horizon from your balcony before breakfast: if La Gomera has vanished, swap this day with day two and take the boat. One thing the tour description will not tell you: the park was the first World Heritage site to be certified a Starlight Tourist Destination, in January 2014, so if the sky matters more to you than the rock, the evening version of this day is the better buy.