Isard (chamois in English and French, and rebeco in Spanish) is one of the most representative mammals of the park. It's easy to watch them near of the high hills (not in the busiest paths).
The best time is early in the morning or at dusk. But it's possible to watch them at any time.
The main problem is how to get to Aigües Torte i Sant Maurici is how to get there without a car.
The only option is by bus. Alsina Graells is the company that covers by bus ther region with a couple or three buses per day from Barcelona to the main towns closest to the National park entry points. The fare range from 22 to 26 euros one way.
From there the best option usually is to hickhick or rent a taxi to the entry points.
From Barcelona the bus departs from
l'Estació del Nord
I think the best way to enter the park it is going to one of their refuges.
On the following link you'll find how to reach them as well as the time from one to other following Carros de foc trek.
All the towns are starting points reached by bus or train. See my tip getting there on public transport to know how to get there.
To visit the park I would strongly recomend you to carry with you a map and / or guide for not getting lost.
Editorial Alpina has good maps / guidebooks of the zone.
You can get the maps in any big bookshop in Barcelona (for exmaple, FNAC) or in the towns closest to the park.
Covering the Park:
Vall de Boi
And the guidebook:
Guía Parque Nacional d'Aigüestortes i Estany de Sant Maurici
The best way for visiting the park is following the "Carros de foc" trekking.
Carros de foc is a trek that covert the main parts of the Park.
The trek can be done in several days sleeping in the refuges of the park.
For those really on fit, they can try to do it on its Skyrunning version, which means in less than 24h, Not easy stuff, 60km, 9200m total uphill and and average altitude of 2400. Only avaible during last week aug and first half september.
For all the information check the web below. There, you'll find how to book the refuges and their prices, how to get there, stimate time from one mountain hut to other, and so on.
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