The guide I had gave the route being 15 Kms from Laruns to Gabas, that link does as well. I'm going to disagree, I'm pretty sure its 20+.It was tough going,I started at 8am and apart from taking a break for 30 minutes in a Eaux Chaudes I was constantly at it. As it says it's a very narrow gorge, and it's covered in lush vegetation. There is no straightish path taking you constantly forward sometimes you go are going backwards, sometimes zig zagging, sometimes clambering down a slope hoping your backpack doesn't give you that extra momentum when you hit the path/ledge.It definitely felt like take a step forward then take two steps back kinda day , I remember using a guide cable to hold on to at one point as I went along on a narrow path with a steep drop. You are never more than 40-50 metres from the road which connects Spain and France, but it feels like it might as well be on another continent, on the 2nd half there is usually a drop to the fast flowing river between you and the road. I'm not usually bothered about walking alone, I become absorbed with the details and the efforts of the moment but there was a few times on that day I wished I was with another person for safety. Ironically when I got the taxi the next day, I realised that I had got the worst bit out of the way and going over the Pyrenees would have been easier than the previous day of the lead up to it, the upper level pastures looked stunning from the taxi.