Sintra

Sintra needs a day trip from Lisbon (40 minutes by train): Pena Palace (a colorful romantic castle) and the Moorish Castle take up the whole day. March-May brings mild weather, though Sintra tends to be cooler and cloudier than Lisbon due to its mountain microclimate. It's cheaper than Lisbon as a day trip, though tickets to the various palaces add up quickly. It's a UNESCO World Heritage Site for its unique concentration of 19th-century romantic palaces and castles, built by Portuguese aristocracy as a summer retreat from Lisbon's heat.