This one was my first real l-o-n-g stalled cairn. I had already seen Unstan and Taversoe Tuick which are both essentially round cairns with stalls, but Blackhammer was different. Like the others, it has been topped with concrete to protect it but the construction and its length is what wowed me. (I hadn't yet seen Midhowe.) I paced it out at 12 1/2 ms!