We stayed in Coimbra for 2 nights and I booked Casa Pombal by looking at Tripadvisor. I think previous reviews are pretty accurate in that you may or may not like the place depending on your personality.
It IS the only guest house in the old part and is quaint and quirky - lots of narrow internal staircases and fun decor. The rooms are basic but adequate. Bathrooms are clean but remember to ask for an en suite if you dont want to share one with another guest. There is clearly a drains problem in this part of Coimbra in the hot month of August as there was a bit of a smell in the bathroom unless windows were wide open. Nothing to do with internal cleaniiness which was good. As my husband says "If you like the smell of eau de toilette - llterally - this is the place for you"
The staff were extremely friendly - very chatty and warm which was lovely. Coimbra was an interesting town but we caught it on an exceptionally quiet 2 days - a sunday/monday also national bank holiday. I think when the students are not around in August the town is also rather quiet and not like its normal self.
If you come by car, make sure you park somewhere not too far away that is free - lots of cobbly hills to hike up wiht bags otherwise.
On reflection and compared with some of the other places we stayed in Portugal i think it is qutie overpriced as casa pombal knows it is unusual in its location,
