Dun Ringill is from Jethro Tull's 1979 album Stormwatch. Ian Anderson wrote it about a historic spot on the Isle Of Skye, where he was living at the time. This lesson was suggested on the Recommend A Lesson thread on the TG Forum.
It features his signature guitar style fast picking, a combination of cross picking and alternate picking. This is a good place to start if you are interested in other songs of his because it is only a couple of tricky measures.
It is played with a capo at the third fret and the chord shapes are all very basic but it is challenging to get it up to speed.