In reply to Andy Nisbet:
Interesting, as a relative local to Lochnagar, I've never sought this out, even though I knew of it. The Smith-Winram bivy/howff is pretty weather-proof, suggesting that the Lochnagar howff may be quite good.
How many cairngom howffs frequented in yester-year are being forgotten with the march of time?
The Dey-Smith howff is also weather tight (though I wouldn't go looking for it in winter), while the Dubh Loch one never appealed to me, I've spent a solo-winters night under rock beneath the Stuic (which was entertaining as a ptarmigan flew into the side of my head while walking in by head torch (......what the feck was that!), and Shelter Stone with it's surrounding second-best(s) are well known.
In Affleck Gray's 'The Big Grey Man of Ben Macdhui' there is mention of over 200 howffs. Andy, would you care to list a few?
They might provide interesting pre-winter 'stomps' in the autumn.