I just recently found out that they have a catacomb in Porto, in the Church of Saint Francis to be exact so I decided to check it out. It was honestly better than I expected. We aren't allowed to take pictures inside the church so you're just gonna have to take my words for it: it was magnificent. The church has a lot of religious arts, a mixture of paintings and wooden sculptures. The church itself is also rich in history; once Napoleon turned it into a horse stable on his siege of Porto. Next to the church there's a museum with a catacomb underground. The catacomb is actually larger than I expected and well kept. Overall it's a 10€ well spent and I'd highly recommend you to visit!