A dream destination around Lisbon (around 2 hours trip - one train + one bus) is definitely Cabo da Roca, the most western point of Europe.
The landscape it's so breathtaking and the way of the ocean merge with the sky seems incredible.
Unfortunately there is no arranged way to go down to the ocean, so you can only see everything fom the top of the mountain. Either way, me and my friends found a way to jump the fence that goes around the belvedere spot and went exploring the area on our own, climbing the mountain.
I admit the path we found was very narrow and very wild, even stopped and transformed itself into a rocky water path down the mountain, but we kept going. At some point we were actually on the verge of the abis, but that didn't stop us...the view was absolutely amazing, and we really wanted to find a way to get down to the virgin beaches (we eventually found it, but it was very abrupt and we didn't have the right shoes to climb it).
Anyway, after a 4 hours walk on the mountain we decided to get back in town to eat something and get some rest aka another 40 minutes walk on the side of the street.
So if you ever want to visit Cabo da Roca, bring in your climbing shoes, your camera, and lots of energy because it's definitely worth the effort!