The Reservoir is just north of the town and, to get to it, you have to pass through Puigcerdà's main shopping area, which gives you the opportunity to see the more modern parts of the old city. The Reservoir has some swans and a well-maintained park. Its a beautiful site when you see it against the backdrop of the mountains and a perfect place to enjoy the natural scenary without trapsing through a private farm.
The church in Puigcerdà is nothing spectacular, but if you do visit the city it is interesting to see the Mediaeval bell tower, which stands near the main parking area. Again, nothing spectacular, but certainly something to see if you're up in Puigcerdà for the natural beauty.