The Mirador del Rio is a viewpoint on the northern tip of Lanzarote, perched on a 475-metre cliff overlooking the strait (the "rio") that separates Lanzarote from the small island of La Graciosa. The views are breathtaking -- the turquoise water below, La Graciosa's sandy beaches, and on clear days the silhouettes of other islands on the horizon.
The building itself is a César Manrique creation, cleverly built into the cliff face so it is almost invisible from the outside. Inside, curved glass walls frame the panorama, and there is a small cafe where you can sit with a coffee and take it in. There is an entrance fee, but if you prefer not to pay, a short walk along the clifftop to the left gives you a view that is nearly as good.
The drive up from Teguise is worth the trip in its own right, winding through volcanic landscapes with several other viewpoints along the way. The whole excursion makes an easy day trip from Puerto del Carmen.