Núcleo Arqueologico da Rua dos Correeiros
Amid the tourist shops and upmarket shopping boutiques of the touristy Baixa district is one of Lisbon's most extraordinary marvels hidden in plain sight under a Millennium BCP bank. Here, a maze of tunnels leads to the remarkably preserved ruins—some dating as far back as the Iron Age–and the remnants of a Roman sardine factory. Fundacão Millennium, the bank's philanthropic arm, sponsors captivating archaeologist-led tours on the hour. Reservations are essential.