This is an impressive ruin mostly hidden behind trees, it is apparently sometimes used by the local sheep.
"The castle, consisting of four storeys and a garret, was as much a palace as a castle, as James Douglas, 4th Earl of Morton, Regent of Scotland, intended to retire here from worldly business. The castle is of exceptional interest because of its design as a "double-tenement" with a wide central corridor running through the building from end to end on every storey. This opens up suites of apartments off it on either side. The castle has a round tower, 25 feet (7.6 m) in diameter, attached to each of two diagonally opposite corners. Each tower has two gunloops, preventing enemies from approaching the walls." (from wikipedia)
Drochil is unusual because unlike most castles where you walk into a main hall/courtyard, here you walk along a corridor and have rooms off to either side. On the ground floor, which I believe was the basement, you can still enter all these rooms.