Hi, just seen your post - I did this trip a couple of years ago, and recommend it. There are 2 trains a day from Zaragoza to Canfranc, at 06.59 and 15.35, both taking 4 hours. Buy your ticket from a machine at Zaragoza Delicias station - no need to book, the train is usually very uncrowded. I stay at the Puerto Husa hotel in the station itself for an early departure. You can get a connecting coach laid on by SNCF (the French closed their side of the railway line in 1974)from Canfranc (it doesn't go through a tunnel) to Oloron St Marie, train from there to Pau. Just remember that it's cold up in the Pyrenees in October - I went in November and there was heavy snow! Good luck.
At the Weekends everyone enjoys the freedom of the outside, especially the Spainish who love to go to the parks and enjoy the good weather and to walk along the many streets with lots af bars and reaturants.
In the sunny mornings you can go to the 'Parque Primo de Rivera' and take a relaxing walk between trees, water and flowers. Stop in a terrace and drink something.
If you have more spare time, plain a one day trip to visit El Monasterio de Piedra (100 km.away from the city) and you will find there more than 50 water falls in a real Paradise of trees, mountains and water surronded by desertic landscape.
If you prefer culture, remember that you have in Zaragoza downtown several museums and Roman ruins( including the river port, the theatre and the walls).You can see Goya paintings in La Cartuja and Muel and a complete collection of 'mudejar' towers in the city.
The tiny fountain on Plaza de Nuestra Senora del Pilar counterbalances the grandiose size of the square and basils.
TORRECIUDAD: it is a shrine built in the XX century. It is worth visiting. Further info: www.torreciudad.org