The reason is snow. The west side of the Col du Tourmalet is closed, so the direct route from the Col d'Aubisque cannot be ridden. This necessitated a longer detour, via Lourdes to tackle the Tourmalet from the East, going back down the same way.
There was nearly an even longer detour. The short, high road between the Aubisque and the Soulor (essentially the way down the Aubisque) was shut at all traffic... except cycles. Phew!
Oh, and did I say it's hot? I mean brain-boiling hot.
Toughest? Probably not. Tomorrow? Tomorrow is longer, but with less ascent and split over four cols rather than just two monsters. I can't wait.