I’m just back from the ride Garry Lager describes above – that loop (we did it clockwise) is pretty hard going, and we had decent weather.
We cycled a loop from starting and finishing in Aviemore, going into the mountains, with an overnight bivvy stop near Derry Lodge. Total distance ~50 miles, total calories ~10k.
The route was 95% ridable the 20 miles to the Fords of Avon bothy. Then we entered the Lairig an Laoigh glen, where the singletrack became quite rocky and it was hard to get a flow, and long sections of pushing/carrying. Once we’d passed the Hutchinson bothy (and into Glen Derry) the trail became flowy with sweet rooty singletrack.
From Derry Lodge area, the Gleann Laoigh Bheag started off with some nice techy climbing across water bars and exposed granite, which lasted to the Corrour bothy. As we gained height up the Lairig Ghru the trail became increasingly rocky with boulder fields at the summit of the climb (Pools of Dee) – pushing/carrying is the only options for extended sections. Once you descend to the tree line the lovely rooty and rocky singletrack starts again, and out through the Rothiemurcas estate back to Aviemore.
However I didn’t get to ride the last 10 miles as my frame cracked behind the headtube – game over for me!
Google map of route: http://goo.gl/maps/XLK92