2 Best Sights in Foz do Douro, Porto

Architecture buffs intrigued by Álvaro Siza Vieira's work after visiting the Museu de Arte Contemporânea might consider a trip to this modernist teahouse and restaurant, wedged between boulders just steps from the sea. One of Siza's earliest projects, completed in 1963, it was designed after careful analysis of the surrounding rock formations, tides, and flora. The approach—a series of platforms, steps, and bifold doors—provides a sense of anticipation and views of the structure and the ocean beyond it. In summer, the enormous windows slide down, creating the impression you can step right out into the sea. At the award-winning restaurant you can take in glorious sea views as you tackle huge plates of seafood and grilled fish.  To visit the interior of the house you must reserve ahead.

The city's top children's attraction, this well maintained aquarium is at the western end of Avenida da Boavista. Sharks, jellyfish, rays, and giant turtles are among the 5,600 or so animals on display, representing hundreds of species. Other highlights include Portugal's only Ocean Tunnel, which gives a peek into underwater life for the colorful creatures that inhabit the main tank. The nearby Parque da Cidade, a large landscaped park dotted with trees and lakes, is a lovely place for a picnic.