The William Herschel Telescope located on La Palma, Canary Islands is (guess what) named in his honour.
Why build such a large telescope on top of an island volcano you ask? The answer is seeing. Hey I just read about seeing in Phil Plaits book Bad Astronomy. Island volcanos are ideal for optical astronomical telescopes because the high altitude places the telescope above most of the water vapour in the atmosphere, and the ocean location combined with the roughly conical shape of the island means that turbulance caused by wind flow over the site is minimized. This combination makes for some of the world’s best seeing. No surprise then that La Palma in the Canary Islands and Mauna Kea in the Hawaiian islands host some of the worlds best optical telescopes.
The images these large telescopes produce is further improved by the use of adaptive optics. Here the mirror in the telescope is mechanically deformed in such a way that the deformation dynamically compensates for atmospheric distortion.