Mains House (possible) (site of)
According to Margaret Warrender writing in “Marchmont and the Humes of Polwarth”, the Hume family lived in a property called Mains House, possibly in the 16th century. This may have been a castle, but as yet I haven’t found any other references to it.
In Joan Blaeu’s Atlas of Scotland, published in 1654 but based in part on Timothy Pont’s maps of the late 16th to early 17th century, Redbraes Castle appears as Ridelbraes. Interestingly it is shown as two castles side by side, each within their own enclosure.
One appears to be in the known position of Redbraes, while the other appears to be further to the east, standing closer to a river – possibly the Howe Burn. It’s tempting to identify the second castle as Mains House.
Warrender describes the location of Mains House as being “near the eastern end of the great avenue”. Interestingly towards the eastern end of the Great Avenue is a defined terrace above a bend in the Howe Burn, so for now I have placed the location of Mains House here.