A grassy mound right beside the road with a few stones poking through the grass, but I don't think this one has been excavated.
Driving north there is a small layby immediately after the entrance to Borrowston quarry and I parked in there and visited both the Borrowston broch and Brounaban brochs in one outing. There is a low barbed wire fence on each side of the A9 to negotiate for each broch, but an old jacket draped over the barbed wire made that easy enough and they were both low enough to simply swing a leg over.
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Borrowston broch photographs
Disclaimer: Some brochs were built with military defensive purpose, and as such can be situated in extremely dangerous areas, such as on the edge of cliffs and ravines. Additionally, these are Iron Age structures, most of them in ruins, and they are extremely hazardous, with crumbling stone walls and hidden chambers. Existing walls, lintels, and passages could collapse at any time. The information here is provided free but it is your responsibility to ensure its accuracy, ensure your own safety, and acquire permissions for access where necessary. Accessing brochs is done entirely at your own risk.