It's necessary to take a bus up to this church, but it's worth the trip. The views of the city and surrounding areas, and of the sea, are stunning on a clear and sunny day. The building itself is attractive - not very old looking on the outside, but inside it feels like it could be 1000 years old (though it's not!). 30 mins is plenty of time to explore this place and take in the view.
NB lots of stairs.