There are whale and dolphin watching boat excursions from Puerto Colon, Playa de las Americas. The one we did - on a Freebird catamaran - was very good. We only a half day but a light salad lunch was provided on board and there was a short stop for a bit of swimming off shore.

From Los Gigantes, the Flipper Uno boat trip makes a good day out. They've got a website, which I have listed in the past.
Otherwise you are a bit cut off from the main tourist areas.
We have done the usual Mount Teide trip, and got a bus to Jungle Park Zoo.

I agree about Flipper Uno, we did it a while ago and it was brilliant, the scenery around Los G is spectacular. A trip to Masca is good too, but the roads wind around the mountains - not for the faint hearted!

Also, depending on how much you want to spend the local taxis do day trips and have a leaflet.

Have a good time

Thanks for all the replies so far. I'd forgotten about Masca, I think I went there once before.

Masca is certainly not for the fainthearted.

What made it worse for us was the aggressive driving of tour conductors taking parties on Jeep Safaris.
They were all showing off and came close to pushing any other vehicles they met over the edge. Our little Clio would not have had a chance.
We complained to the particular company (the name was all over the sides of the jeeps) but were told "they only employ experienced drivers".
I had never seen my husband who is an experienced, confident driver so un-nerved.I was terrified.

That was three years ago so hopefully something will have been done to improve that situation by now.