This route covers Porto, a Douro Valley day trip, and Braga, using regional trains that make the whole loop possible without a rental car. It's paced for someone who wants to actually see things, not just check them off.
Days 1–3: Porto
Three nights lets you cover the Ribeira riverfront, a port wine cellar tour across the river in Vila Nova de Gaia (many tastings run $8–12), and the Livraria Lello queue on a weekday morning when it's shortest. Base in a hostel in the Bolhão or Cedofeita area for $16–20 a night.
Days 4–5: Douro Valley day trip
Take the regional train from São Bento station to Pinhão (about $14 round trip) rather than booking a $70+ organized tour. The train ride itself hugs the river and is one of the more scenic rail journeys in Europe. Spend the day in Pinhão and Peso da Régua before the last train back.
Days 6–7: Braga
An hour north of Porto by train ($4 each way), Braga is Portugal's oldest city and noticeably cheaper than Porto for food and lodging. Bom Jesus do Monte, with its zigzag staircase, is reachable by a short bus ride or a steep but doable walk.
Takeaway: Book the Pinhão train yourself instead of a Douro Valley tour package — it's a third of the price for the same scenery.