This flat definitely needs an AC for those hot summer days where the heat is unbearable even at night. Our stay coincided with the summer heat (30+ degrees) and June festives in Lisbon when the entire Bica district was partying every night until 4 am in the morning but we couldn't close the windows because the flat would become too hot with windows closed. It was a miserable experience for us at night during the 4 days of our stay but an air con would have made it less painful for us. In other seasons this flat might be a good value, or if you don't mind staying up late / partying all night. The flat itself is conveniently close to central Lisbon and clean, with all the necessary utensils in the kitchen and an iron. It can comfortably sleep 3 adults (4 would be a stretch if the 4th person doesn't mind sleeping on a couch).