Beautiful apartment, spotlessly clean, large and excellently maintained.
The photos don't really do this apartment justice as it looks better than it does online. It's large, light bright and airy and is perfect for 4 people to stay comfortably for any length of time. The air con is fantastic and the flat was immaculately clean, from the cutlery to the bathrooms. Linen and towels looked like new and couldn't fault the apartment.
Just to be aware, the apartment is on the top floor and the only access is by several flights of stairs so could be an issue if you have mobility problems. The stairs in the middle of the apartment may also be problematic with small children as there is no real way of blocking them off. The front door is also sometimes deadlocked so make sure you have keys to get out of the building or you may get locked in. The wifi was also quite weak, but really that's being picky, as this flat is great and I would happily stay again.
In terms of location, it's very easy to find and very close to a lot of the sights. Porto is very hilly and this is at the top end of quite a few of those. Although I wouldn't let it discourage you, as its part and parcel of the trip, plus you can use the metro or a taxi should you choose.