long-standing problem of whether certain stone constructions (like the round citadel at the top of Dunadd) had roofs or not.
Dunadd has been excavated three times: in 1904-5, in 1929, and in 1980-1. The most recent excavations were the most interesting. They established the sequence of construction of the features and rough dates for the phases. They also found lots of pottery imported from France, which presumably arrived full of wine, an interesting look into overseas trade in the Dark Ages.
The most recent archaeologists dug only four trenches, two of which were pretty much empty. But one landed on top of a metal-working shop of the 7th century and produced wonderful things: more than 200 crucibles, hundreds of molds and mold fragments, and numerous pieces of bronze, silver, and gold. I would love to show you pictures, but so far as I can tell there just aren't any. Grrrrrr. One day British archaeology will enter the internet age. I hope this happens before I die but I am not counting on it.