A network of tunnels underneath the Banco Comercial Portuguesa, they are believed to be the remnants of a Roman spa circa 1st century AD. Guided tours are offered by the Museu da Cidade; phone ahead of your intended visit to book.
Tel: +213 211 700
Address: Rua dos Correeiros 9
Opening Times: 10am-noon and 3-5pm Wed and Sat
Admission: tours free