Cycling in Lisbon: An Honest Assessment From Someone Who Tried
Lisbon is a cycling city the way a cobbled staircase is a running track. Technically possible. Not recommended without qualification.
The city has been investing in cycling infrastructure since around 2015, and the flat areas — the waterfront from Belém to Cais do Sodré, the Avenida da Liberdade, the riverfront promenade in the Santos and Alcântara direction — are now genuinely cycleable. The GIRA bike-sharing system (gira-bicicletasdelisboa.pt) covers most of the accessible routes and the app is functional. A day pass is €2. A monthly subscription is €2 for 45 minutes of free use per trip.
The hills are the honest limit. If you are staying in Alfama, Mouraria, Bairro Alto, or anywhere elevated, the electric GIRA bikes are the only practical option for the uphill segments. The regular bikes will defeat you before you defeat them.
My recommendation for visitors: the waterfront route from Belém to Cais do Sodré on a GIRA bike is one of the better things you can do in Lisbon on a clear morning. Flat, scenic, the Tagus on one side and the old industrial buildings on the other. About 8km. Takes 35 minutes at a comfortable pace. The Tower of Belém (torrebelem.pt — Av. Brasilia, Belém) is at one end. LX Factory (lxfactory.com) is near the other. It is a good morning.