Yes, three days is the right amount of time for Lisbon, and it is the length we recommend for a first visit. It gives you two full days in the historic center, covering the castle, Alfama, tram 28, the miradouros, Baixa and Chiado, plus one dedicated day for Belem, which deserves more than the rushed half-afternoon most people give it. With three days you eat well twice at night without repeating neighborhoods, fit a fado evening and a Bairro Alto night, and still ride out to the Jeronimos Monastery, Belem Tower, and the custard tarts at their source. What still gets cut: the Gulbenkian Museum, Principe Real, and any Sintra day trip, all of which need a fourth day. This duration suits first-timers, couples, and anyone building a Portugal route with Porto next. Stay in Baixa-Chiado for the transport links, since the tram to Belem leaves from its doorstep and both center days start on foot.