@ndnorton – I’ve not ridden in les arcs but destination x is just what they say it is a week of riding deserted single track, aside from warm up day at la Saises bike park we saw 3 or 4 other riders in a week. Lots of long descents 1000m plus and a fun combination of lifts, van up lifts, a bit of pedalling and bus/van transfers back up from valley. Look up Areches Beaufort for altitude, it’s a charming village, unspoilt with old villages houses complete with vegetable patches, definitely in the mountains as such. There are far more walkers and roadies than mountain bikers.
Link to photo set from fellow stw-er (much better photos than mine !) Destination X