When you pass through Gondar, you really shouldn't miss seeing the fort of Fasil Ghebbi. A UNESCO World Heritage Site, these fortifications are amazing. With crenels and towers, you'd think you were in Europe. You can walk in the gardens, admire the building's exterior and take a look inside some of the 5 palaces.
If you're about during Timkat (January), you can also attend the religious celebrations which take place at Fasiladas' Bath. The pool is filled with water and a crowd, dressed in white, comes to be blessed. For the rest of the year the pool is empty, but the site stays open and is still a POI all the same.
Two other places intrigued me: the Debre Berhan Selassie church, very well-known across the country and located on a hill in the north. Upon entry, you can admire very beautiful paintings on the ceiling and walls. Also, the Qusquam Monastery, built by Queen Mentewab, as well as her palace.