The rule we made on the plane: one thing a day that she chooses, one thing a day that I choose, and nobody sulks about either. It survived four days, which in the company of a fifteen-year-old is roughly a diplomatic triumph.
We stayed in Príncipe Real, which is the version of Lisbon I'd recommend to any mother travelling with a teenager — leafy, residential, gently expensive, on a plateau rather than a hill, and close enough to Bairro Alto that she felt like she was somewhere, far enough that we could sleep. A room with two beds and a balcony is the whole brief. The balcony is where she sat with her phone at seven in the evening while I got ready, both of us in the same square metre of air, not talking, entirely content. Ask for a room off the street. Ask whether breakfast runs late; teenage sleep is a geological force.
What worked, in order of how often she has mentioned it since. The tram 28 at eight in the morning, before the queues, when it's still full of people going to work and the driver rings the bell at a cat. The Miradouro de São Pedro de Alcântara, with two custard tarts and a paper napkin each. LX Factory on a Sunday, where the bookshop with the red staircase — Ler Devagar — did more for her reading habit than three years of my recommending things. The Gulbenkian gardens, which are free to walk through and full of ducks with strong opinions. A ferry to Cacilhas for the ten-minute crossing and a plate of fried fish on the other side, because a boat is a very cheap adventure.
What worked for me, which she tolerated: the Museu Nacional do Azulejo, out along the river, where the tiles do the same blue over five centuries and she found, unprompted, the one panel she liked. An hour in the Feira da Ladra flea market on a Tuesday, where she bought a brass key for two euros and still has it.
The safe, practical part, since that's the question everyone actually asks. Lisbon is a walkable, low-drama city with one real irritation: pickpockets on tram 28 and in the Baixa crowds. We kept phones in front pockets, cash split in two places, and a rule that whoever was navigating held their phone with both hands. The hills are steeper than they photograph — the Elevador da Glória and the Santa Justa lift are not tourist gimmicks, they're transport. Teens are safe out on their own in Príncipe Real and Chiado in daylight; we agreed on a two-block radius from the hotel and a text on arrival, and that was the extent of the negotiation. Trainers, not sandals: the cobbles are polished to a shine and they are slippery in the rain.
The thing about travelling with your own teenager is that the itinerary matters far less than the hours in between it — the queue, the tram, the balcony, the second tart. What we brought home was not Lisbon. It was the version of each other that only exists away from home.

