Prince of Wales Shaft at Phoenix United Mine, built for the last big pumping engine made in Cornwall (1907). It’s an impressive and distinctive landmark with great views across the countryside.
Re the Tin MIne - I believe most of the mines around Caradon Hill were primarily copper mines. I could be wrong here. Tin was sometimes found below the copper (and searched for when the copper ores ran thin) but was rarely found or worked in quantity. Still, the description "tin mine" is often used to describe a disused engine house and or chimney so I'm being a bit pedantic!