The monument consists of a 15th-century L-plan towerhouse, with an underlying prehistoric fort.
Auchindoun is attributed to James Cochrane, Earl of Mar, or Thomas Cochran, favourite of James III. By the 16th century it belonged to
the Ogilvies, who sold it to the Gordons in 1535. By 1725 it was derelict, and William Duff of Braco was granted permission to remove stones from it for his new house at Balvenie.
Built on the L plan, it is unusual in having the entrance not in the re-entrant angle but towards the W end of the S wall. It leads into a barrel-vaulted basement, with a drain in the W wall and a small barrel-vaulted chamber (2 x 1.7m, and 1.7m deep) below the floor.
This chamber was accessible from the first floor by a stair in the NW corner, but there was no direct means of communication between it and the cellar beneath the jamb, which would only have been accessible
from above, possibly through a trap door; it may have been a prison.
On the first floor was the hall, 9.3m long by 5.8m wide. The stair emerges at the SW corner of the screens end. In the adjacent W wall
is a wall closet. At the E end of the screens passage another door
leads into a jamb-chamber, with garderobe and window seats. This may have been the steward's quarters, supporting the idea of the chamber below having been a prison. The hall was rib-vaulted in two bays, the vaulting springing from corbels; at the N end the angle-groins were incorrectly set out, so that an intermediate capital had to be
inserted to enable a fresh start to be made at a higher level. At the
N, upper, end of the hall is a large fireplace, flanked by windows
with stone seats in the E and W side walls.
The floor above may have been an upper hall, with large windows. In
the jamb there were two storeys in the height of the hall, and other rooms above. It is not clear how they were accessible.
The tower was surrounded by a high wall measuring some 22.4m E-W by
32 m N-S. On the south this contained the gatehouse range. On the E
the wall was later pushed out some 6.5m to accommodate another range containing kitchen, bakery and other offices. A rounded tower with gun-loops was also added to the NW corner.
The castle stands inside a bivallate hillfort, assumed to be of Iron
Age date. The inner rampart of the fort, formed by a ditch and outer bank, is mutilated by approach ramps to the castle on the W side and
by quarrying on the S. The outer defences are formed by natural rocky slopes on the E and by a ditch and outer bank on the N and S; on the
W the rampart has been destroyed by cultivation. On the E side are remains of a lime kiln of more recent date.
The area to be scheduled includes the remains of the castle, fort and lime kiln, representing an irregular area some 200m E-W by 230m N-S,
as shown in red on the accompanying map.