I have a flight next week that lands at OPO at 12:30AM. I will be traveling solo, I am 22, female. Is it safe to sleep at OPO and take the metro to city center in the morning, or should I just book a hostel and take a metro from OPO to the hostel when I land at 12:30AM? How safe is the metro vs. the airport?
The metro stops running at 1:00 a.m., so if your flight is delayed then that is not an option. If you are really concerned about your safety, then IMO you would be best to book an inexpensive hotel near the airport for the night. Head to the city center the next morning after a decent night's sleep. (which you will not get if you are sleeping in an airport)
I've never been to the Porto (but I've been to Oklahoma...you are too young to remember Three Dog Night's I've never been to Heaven, lol) but I have used this website when I wound up with an unexpected overnight at the Atlanta airport a few years ago.
https://www.sleepinginairports.net/guides/porto-airport-guide.htm