Time's Castle is a gigantic, grim, dark construction that exists in Underland and is inhabited by Time, that owns and rules the place. It has a predominant black color, which matches its ruler's outfit. Both inside and out, the castle possesses a grim, dark, uninviting aspect, which may reflect its owner personality or intentions.
When seen from the sky, the construction itself seems to act like a clock, with three gigantic hands (seconds, minutes and hours) protruding from it and pointing to giant roman numerals. There is an abyss separating the castle and the rest of Underland, and the only way to access the construction on foot seems to be by jumping on the giant clock hands.
Inside the castle, the chamber of the Grand Clock keeps the Chronosphere.