This weekend Porto has several urban markets all over the city:

   

Urban Market – Spring is Coming: March 10 to 12 , from 11 am to 7 pm @ Hotel Carrís Porto Ribeira

Mercado Porto Belo: March 11, from 10 am to 7 pm @ Praça de Carlos Alberto

Flea Market: March 11, from 2 to 7 pm @ Praça de Velásquez

Sensations Market: March 11 and 12, from 11 am to 7 pm @ Parque da Cidade

(pictures taken from here)