I’m looking to explore architecture and nature on my own :-) where would you recommend Lisbon or Faro?

I’m looking to getaway and reconnect with nature and experience Portugal on a small budget.

Please let me know what is a MUST SEE and where you would land either in Lisbon or Faro..

I was looking at Quinta Da Regaleira in Sintra it is beautiful! What is the best way to get there from Lisbon

Also any itineraries you have will be very much appreciated so I can start planning

Thanks any help is appreciated.