For most travelers, one full day (at least 8 to 10 hours) is the absolute minimum required to see the "essential" highlights of Sintra, such as the colorful Pena Palace, the Moorish Castle, and the mystical Quinta da Regaleira. Because Sintra is located in a hilly, forested area with sites spread out from one another, navigating the narrow roads and waiting for the tourist buses (like the 434 line) can take up a significant portion of the day. To truly appreciate the romantic architecture and lush gardens without feeling rushed, many travel experts recommend staying two full days. A two-day itinerary allows you to visit less-crowded gems like the Palace of Monserrate, the Convent of the Capuchos, and the Sintra National Palace in the historic town center. If you are a fan of slow travel or photography, spending a third day allows for a deep dive into the surrounding Sintra-Cascais Natural Park and the dramatic Atlantic coastline at Cabo da Roca. Regardless of the duration, arriving as early as possible (before 9:00 AM) is vital to beat the heavy crowds that arrive by train from Lisbon.