A veritable wonderland of caves, grottos and underground walkways set within a sprawling garden landscaped in the image of the cosmos, Quinta da Regaleira is one of the most surprising and bizarre visitor attractions in Sintra. Its given name refers to the summer residence of the Carvalho Monteiro, a mansion-palace exuberantly decorated with turrets, towers and panoramic terraces. Dating from the late 19th century, the building is an extraordinary example of the Portuguese neo-manuline style of architecture and its interior is fascinating to explore. But if you've youngsters in tow it's the grounds that will mesmerize inquisitive minds, and the imagination will run riot. Let them play hide-and-seek, discover lakes and waterfalls and then follow the castellated walls enclosing the estate. Afterwards, relive the adventure over refreshments at one of the café tables facing the main house.