Indeed it looks like a tunnel . Never have seen this mor heard of it
it is in the rua da Fábrica
i found this on a website of the municipality of Maia from 2020
The connection, which essentially serves the populations of Vila Nova da Telha, Perafita and Lavra, in the municipalities of Maia and Matosinhos, underwent requalification and expansion works and reopens this Friday, at 6 pm, reports Jornal de Notícias.
The Tunnel under Francisco Sá Carneiro Airport reopens now with another 150 meters in length.
“It is an important link for the local population who, for more than a year during the work, had to go around the airport on their daily journeys. A call that used to take five minutes became 15 or 30 minutes, depending on traffic”, explained to JN Joaquim Azevedo, president of the Vila Nova da Telha Parish Council.
The Maia City Council emphasizes that, with this tunnel, the reopening of the continuation of Rua da Fábrica through the Airport Tunnel and its alignment with Avenida Gago Coutinho, which allows the restoration of access to Vilar do Senhor.
The municipality adds that the renovated airport tunnel has a sidewalk, which allows pedestrians to pass.
It should be noted that the intervention is part of a project to improve the airport's terrestrial communications, budgeted at 15 million euros.