Sintra receives millions of visitors a year at Pena Palace, Quinta da Regaleira and the Moorish Castle, but most are day-trippers who come by coach from Lisbon and fill the town between 10am and 6pm. There are queues at Pena, and entry is now by timed ticket. That is your strongest selling point: people who stay in Sintra visit the palaces early in the morning or late in the afternoon, away from the coaches, and swap a rushed day trip for a calm visit. Two nights are enough to combine the palaces and the Atlantic coast.
We build websites with our own code and no WordPress for short-term rentals in Sintra, São Pedro de Sintra and along the coast at Colares and Praia das Maçãs, with direct bookings, in Portuguese and English (without English you won't sell in this Greater Lisbon market), plus Spanish, French and German, and local SEO for searches such as 'Sintra accommodation near the palaces' or 'Sintra two-night house'. On your own site you can explain what makes someone stay: waking up near the palaces and getting into Pena before the coaches arrive. A Booking listing doesn't explain that.