Hermit's Castle in Achmelvich, Scotland is believed to be the smallest castle in Europe. This quirky Brutalist-style structure, built in the 1950s by architect David Scott, stands out with its angular shapes and pebble-and-shell design. Legend has it that Scott spent six months constructing the castle in secrecy, only to spend a single night there before disappearing back to Norwich. Visitors can explore the tiny interior room with a concrete inset for a mattress, making it a truly unique and mysterious spot to visit in the Scottish Highlands.