Yes, Sintra is absolutely worth a day trip from Lisbon in 2026, though it requires careful planning to avoid the heavy crowds. As a UNESCO World Heritage site, it offers a concentrated collection of "Romanticist" architecture, including the vibrant Pena Palace, the mysterious Quinta da Regaleira with its initiation wells, and the medieval Castle of the Moors. In 2026, the experience is enhanced by a new mandatory reservation system for Pena Palace, which has helped regulate the flow of visitors. While you can't see all six major sites in one day, a well-structured trip (focusing on 2-3 landmarks) is highly rewarding. For the best 2026 experience, travelers are advised to take the 40-minute train from Rossio Station rather than driving, as parking in Sintra’s narrow, winding streets is nearly impossible. The sheer contrast between Lisbon's coastal vibe and Sintra's misty, forested "fairytale" atmosphere makes it a 2026 "must-do."