Sandra, I'm currently in Burgos--a very attractive city. Perhaps this information will be of some use. I think these sre cosidered the three major religious sites.
The Catedral is in the center of town, as usual. It's open daily at least 9:30 AM to 6:30 PM, but probably 6:30 is the latest entry time, not when they throw you out. I spent 2 hours inside, but I used the self-guided English audio tour, and if I pay to see something, I'm for sure going to see it. I'm certain most people spend less time there.
The Real Monasterio de las Huelgas is about a mile from the Catedral, easy to locate if you have a map-equipped electoric device that knows where you are, but otherwise it could be a bit tricky since Burgos isn't overly blessed with street signs. Tourist office info states that hours are Mon-Sat 10 AM to 1 PM and 4 PM to 5:30 PM. Sunday hours were reported to be 10:30 AM to 2 PM, but the signage on-site today said Sundays till 3 PM. This site requires a tour (departing frequently), available in Spanish only. I saw no information in English (didn't notice signage in Spanish, either). My group (Sunday around noon) had at least 35 people, and I certainly wasn't going yo waste the time of so many other people by asking the guide to repeat something. The tour lasted about 40 minutes, and we hurried past a few things I would have liked to look at a little longer. Parts of rooms were roped off, so you're couldn't get close enough to see some things well. The overall experience (at 6 euros) was not particularly good for me. That said, there are many beautiful things in the complex, including some Mudejar features and interesting medieval textiles in the museum.
The third site, the Cartuja de Miraflores, is roughly 3 miles from the cathedral. Again, it would be great to have an electronic map for navigation. Tourist office info says the hours are Mon-Sat 10:15 AM to 3 PM and 4 PM to 6 PM; Sunday hours are the same except that opening is at 11 AM. This is a smaller place, but I much preferred the experience here. You go through the church and connected museum rooms at your own pace, using the (optional) 2-euro English guide book. You can walk right up to most of the features to get a good look. There's a really stunning Berruguete painting of the Annunciation in the museum area. Entry is free, but they gladly accept donations. I spent about 90 minutes at the Cartuja, but others were moving through consideranly faster.
