Please give me some ideas for my trip! I am lost!

Ola!

I am a 37 year old recently divorced guy going to portugal to attend my cousin's wedding to a lovely Portuguese woman in Lisbon. I get to Lisbon on June 15th, and will be there until June 22nd. June 22nd - June 29th I am completely free to do whatever I want, before I need to be in Lisbon for my flight back home on the morning of the 30th.

I DON'T want to go to Sintra (Have heard its quite swarmed), Porto (since I am going to be in Lisbon for a good chunk of time I'd rather avoid another large City), or the Algarve (heard its very "young", croweded, "party" kind of place.

I will probably rent a car on the 22nd. I was thinking Bucaco Forest, Conimbriga, Serra Da Estrela, Monsaraz, Marvao (my cousins fiance helped with these ideas).

What I am after:

a) experience Portugal without TOO MUCH crowds (I realize Portugal is swarmed with tourists in June so I do not expect to be in some super secret "no tourists" zone I am not unrealistic)

b) maybe guided tours/hiking tours with similar aged tourists. Do you guys know how I can find such groups/tours that are well reviewed?

c) a place for quiet reflection/good food etc. Basically not after a party, I want to chill, but also meet people, eat good food etc.

Sorry if this is the billionth post like this, its just I have NEVER travelled like this before: where I am going to a brand new country with so much free time like this.

Obrigado!