Yes, in 2026, virtually all of the major palaces, monuments, and museums in Sintra are open on Sundays, making it one of the busiest days for tourism in the region. Iconic sites like the Pena Palace, Quinta da Regaleira, the Castle of the Moors, and the Monserrate Palace operate on their standard daily schedules, typically from 9:30 AM to 6:30 PM. Most local restaurants and souvenir shops in the historic center (Sintra Vila) also remain open to cater to the influx of weekend visitors. However, it is important to note that while the monuments are open, Sunday is a day when many locals from Lisbon visit, leading to significantly longer wait times for the 434 and 435 tourist buses and larger crowds at the ticket gates. To manage this, it is highly recommended to pre-book your timed entry for Pena Palace and arrive as early as possible. While the tourist attractions are open, some smaller, local-centric businesses or traditional workshops outside the main tourist zone may be closed, but the "fairytale" experience itself is fully accessible.