The Interallied Memorial
If you are into old buildings and you have a moment to spare, while you're at Guillemins be sure to visit the Interallied Memorial.
It's a mile uphill (just follow the tower that stands to the South) and you will be rewarded with a nice view over the Guillemins quarter. The Memorial was built in commemoration of the first World War (and because of the city of Liège was the first to offer serious resistance to the Germans) but was never really completed. The main attraction is the Church of the Sacred Heart and Our Lady of Lourdes (but since the Liegeois are not really patient, they call it the Basilique de Cointe, although it never really received the title of Basilic.)
Neglected for years on end, the city of Liège asked the French Graffiti painter Bonom to paint a fresco on the facade to mask the fact that the church is in dire straits for the festivities of 100 year anniversary of WW I (I am not inventing this one!)
There are plans to renovate the whole site (the city is looking for funders.)