After a week in Madeira in May, 2014, we are considering 5 days in Lisbon, Sintra, and Porto--I read that it's a 3 hr. train journey from Lisbon to Porto; 40 minutes Lisbon to Sintra. Is there a train from Sintra to Porto? My thoughts: Arrive Lisbon Mon A.M., overnight there; leave Lisbon late Tues afternoon, Tues & Wed nights in Sintra; arrive Porto on Thursday and leave on Saturday. Is that too crazy? I had my heart set on seeing the Duoro Valley...and you all have made Sintra sound like a "must do"--and how can we not see a bit of Lisbon? I'll plan specific sights once I discover if it's a reasonable plan to see 3 places in 5 days, or if it's just best to stay in Lisbon or Sintra...or Porto...and do days trips out from there. Any advice? Much appreciated.