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We did cross the region from North to South and from West to East. The whole trip was 561 km long and we did around 8000m of positive altitude difference. It took us eight days. Here are the details:
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Day 2 - Mont Dore - Murol - Condat - 71km - 600m
Day 3 - Condat - Bort les Orgues - Mialaret - 89km - 1100m
Day 4 - Mialaret - Mauriac - Le Falgoux - last turn of the Pas de Peyrol Pass - Le Falgoux - 75km - 1400m
Day 5 - Le Falgoux - Salers - Puy Mary - Lavigerie - 72km - 1700m
Day 6 - Lavigerie - Murat - Prat de Bouc - Saint Flour - 58km - 750m
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Day 8 - St Martin Sous Vigoureux - Neussargues - Massiac - 70 km - 50m
You can see a map of the trip here: http://maps.google.com/maps/ms?ie=UTF8&hl=fr&msa=0&msid=109702653242020781086.00045538f103f756fde10&ll=45.224612,2.71637&spn=1.307721,2.460938&z=9
General: Auvergne is a good cycle touring destination: the landscape is beautiful with a reasonable level of difficulty. Villages you cross are very authentic. There is enough touristic infrastructure and the food is really nice (especially the cheese and meat if you are not a vegetarian like me). The roads were very calm as well we had absolutely no problems with too much traffic. Finally I fell in love with the local cows - Aubrac - which look exactly like the cows in comics that you watch when you're a child.
Day 1 - We were dropped here by car - the original plan was to start in Clermont-Ferrand arrive to Mont Dore on Day one but the weather was bad so we pushed to Mont Dore directly. Mont Dore as well as La Bourboule are typical thermal towns with some nice architecture from the beginning of the century. We stayed in a really nice B&B La Marmotte du Sancy - all constructed in wood - where we also had a nice dinner. We can recommend this: http://www.fleursdesoleil.fr/crans-maisons/63-bouget.htm
Day 2 - the day started with a pass : Col de la Croix Morand (1400m) but that was the only
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Day 3 - this was the sunny day :) we started by going down which was not bad after the dinner Chez Marissou. The road follows the river la Rhue and there are some nice sights on the way down. We went to see the castle Chateau de Val which is situated on the Bort les Orgues dam. Then we headed to Bort les Orgues and climbed up on the "Orgues" (special form of volcanic stone) from where there is a great view over both the Massif du Sancy and Cantal. We then headed towards Neuvic where we stayed overnight.
Day 4 - This started in the rain so what was supposed to be nice - passing by the Dordgne - was all foggy and we didn't see much. We had lunch in Mauriac where we met other cyclists (that's always a good moment). From there we climbed up the valley to Falgoux, we dropped our luggage in the hotel and went up the Peyrol Pass. This was hard but definitely worth it - even though the weather wasn't great. In Falgoux we stayed in the Hotel des Voyageurs http://www.cantal-hotels.com/lefalgoux/hoteldesvoyageurs/hoteldesvoyageurs.htm. Good value for money simple but comfortable and not expensive.
Day 5 - The hardest and at the same time the rainiest day. This was meant to be a series of wonderful views and turned into battle against rain. But never mind we made it. The good thing we did was that we asked a car to bring our luggage on top of Puy Mary and leave it in the Tourism Centre up there while we were doing our round trip through three passes. We went to Salers where we met our friends cyclists from Mauriac... Salers is indeed a very picturesque place. Then we continued to contour Puy Mary and soon after noon it started to rain which it only stopped as we were approaching our B&B after having passed Puy Mary, frozen, wet and without any view.
Our B&B was wonderful (though up-market but worth it) Auberge d'Aijean - we also recommend to have dinner if you stay there but you'd better reserve: http://www.auberge-puy-mary.com/fr,1,3989.html
Day 6 - We stopped in Murat, charming medieval town, went through the Pass Prat de Bouc - nice and very calm road - to arrive to Saint Flour at the end of the day. This was a rather easy part but we needed it. Our bike as well since when we arrived to Saint Flour we were missing five spokes on the back wheel which is the one carrying the heaviest luggage (and me :). This was just in time to find a repair shop as we had no spare ones.
Saint Flour was also a pleasant break - it's just that our hotel was more than ordinary - Hotel de l'Etape...
Day 7 - another quite difficult day with some rain to wash our sweat... this wasn't difficult because of any passes but because of many ravines that where we had to go down just to go all the way up on the other side. We passed by Chaudes Aigues, another thermal town, and followed the road past the river Tuyere. We stayed in a beautiful B&B (also on the expensive side) ; it is a medieval castle in Lescure - really authentic if it fits in your budget - nice dinner as well. http://membres.lycos.fr/psvlescure/
Day 8 - this was our final day - we first wanted to go to Aurillac and take a train here but we learnt in the B&B that there were works on the line and no train traffic from Aurillac so we had to change our plan and head towards Massiac where we were able to take a train for Clermont. The road from Neussargues was busy and not interesting but we had little choice. On the other hand we quite enjoyed to land in Clermont-Ferrand in the evening and rest knowing there was no need to pedal the next day.