Allocation of time in Portugal
 

We are currently staying in Sao Miguel, Azores and just recently visited Madeira. These islands are wonderful. Planning another trip to Portugal mainland. We have visited The Algarve previously and would like to spend time in Lisbon, Sintra and Porto as have never been previously. How much time should we allot in each location in order to have a good look around. And from Lisbon, can we reach the other destinations easily?