Teruel is the site of some of the most impressive Mudejar architecture in all Spain.Examples are:
The Cathedral - impressive from outside but rather a mixture of styles
El Salvador - very decorated Mudejar tower with a plain tower within and a staircase usually open between them.
San Pedro - site of the Alabaster tomb of 'Los Amantes' The Lovers of Teruel. Good Mudejar tower and complete coverage of internal bricks with designs.
Also well worth seeing are;
The aqueduct/viaduct
The Provincial Museum - once a palace. Ensure that you ask the guide on the top floor to let you out to the arcaded exterior for a terrific view of the Cathedral.
Dinopolis is a huge paleontological museum disguised as an amusement park, if you look for amusement you'll be disappointed, but if you like fossils, don't hesitate to go. It's a little far away, though.