Lisbon is my favourite place. It’s not a massive city so ideal to just wander around. We accidentally stumbled upon a few incredible viewing spots where you can have a drink or coffee and look out over the city. Can’t remember the names of the cafes I went to but I remember all of the coffee being nice.
There are a lot of cool bars around Barrio Alto though it can get busy. The PARK bar, that’s been mentioned has good views but was full of drunk English people. My favourite place was called Pensão Amor, in the former red light district - really nice cocktails.
Definitely have a wander through Afalma, the old town. Very hilly but has tiny narrow streets and colourful houses and old trams - you can get nice food from any of the small family restaurants there for mad cheap.
Sintra definitely worth the trip. I went in summer so also checked out Cascais, (20/25 min train away from the centre, for like €4 return). The main highlight there is the beach so not sure if worth it in Feb? Obviously not ideal as you’re vegan/vegetarian but there’s a restaurant there called Moules and Gin which was incredible (worth it for just the gin if you do venture out there).
Enjoy!