It wouldn't be hard to spend an entire day wandering Quinta da Regaleira, a fairytale-like estate in Sintra. Built in the early 1900s, the property belonged to the Viscondessa da Regaleira and was later acquired by Antonio Augusto Carvalho Monteiro (nicknamed Moneybags Monteiro). Monteiro hired the Italian set-designer and architect Luigi Manini to do the landscaping and interiors.
Today Quinta da Regaleira is a UNESCO World Heritage site and visitors can explore its maze of gardens, grottoes, and lookout towers. I spent hours in the castle, marveling over the detail of the woodwork and the enormous fireplaces and chandeliers in the dining room, bedrooms, and living rooms. Make sure to take a map so you don't miss Waterfall Lake or Ibis Fountain.