"Only sun and party?" Isla de Tenerife by Belsaita

Tenerife is definitely a touristy island, specially the south, where German and UK tourist concentrates and there is nothing else than sun, beach and party. But the North part of Tenerife are not so crowded (this zone is not so sunny... so is more green and beautiful).

abouttenerife.com

I do recommend hiring a car and travel around the island. The most beautiful landscapes are in the North. You may visit historic sites as La Laguna and La Orotava. Puerto de la Cruz,even touristy, still has some local feeling and many tourists are Spaniards there. More off the beaten path, nice villages as Masca (at its impressive valley), and Punta de Teno.

Las Cañadas del Teide is an astonishing volcanic area. You can do some good treks here. El Teide is the highest Spanish mountain. It's possible to climb the summit if you get permission at the local tourist offices in advance (not allowed during winter due the ice). There is a cable-car that leaves you near the top, you can see the rest of islands if the day is clear... but be aware that frequently is not working due the strong winds: better ask fist at the tourist office their phone number and call before going, so, if it's closed, go there another day.

Depending on how many of days you stay, you can easily visit other islands as a side trip, as there are many connections with ferries and planes.

And not forget to enjoy the delicious local food, avoid the touristy restaurants (easier to say!) and go to local places in the fishing villages or interior towns. 'Papas con mojo' and fresh grilled fish.... yummmm!