First, regarding hiking in the Pyrenees, which route are you doing? I've spend a fair while walking in that area (I did the full 780km Haute Randonnée Pyrénéenne a few years ago), and my one bit of advice would be
pack light... It's very steep (at least it is if you're doing the interesting routes) and a standard day would often have more than 1000m of elevation gain. This is not the place to be taking a big, heavy photography kit...
Regarding 28mm - I've used the M28/f2.8, which is easy to find, tiny, cheap and performs 'ok', and currently own the M28/f2, which is rare, expensive, biggish and performs exceptionally - it's my favourite 28mm and worth tracking down if you're a 28mm devotee.
I would second others suggestions of the GR. It's incredibly light and compact (I usually have mine in a little pouch attached to my rucksack's hipbelt) and the image quality is astounding. I've used mine as my only camera on long walks in the Swedish Arctic and Iceland and never found myself wanting more.
The Barroude Wall, Pyrenees (unfortunately I believe the Refuge de Barroude has since burnt down) - EM5/25mm Nokton
Above the Rapadalen, Sarek National Park - GR
Þórsmörk , Iceland - GR