I think you will have enough time for the two of them, if you take a taxi from the St.Jeronimo Monastery to the Castelo São Jorge. And do pre-book online your tickets to the Monastery.
Noraatc's point about pre-booking is well made, there can be a long queue. There is a queue on the right for the church and on the left for the Monastery.
I agree that you can perfectly well visit both in a day. There are quite a number of popular attractions in and near Belem but if you are content to see the Monastery and the Tower you do not have to spend more than a couple of hours. Don't bother going into the Tower (again, long queues) but maybe have a look at the Discoveries Monument (Padrão dos Descobrimentos) along the way, it lies between Jeronimos and the Tower. Absent a queue I think it well worth spending a couple of euro and going up the lift to the top. There are great views across Belem and across the river. Also the area around the base of the monument. Don't go up if it is windy and hang onto your hat even if it isn't.
If you decide to try a Pasteis de Belem or three don't join what is always a long queue outside, that is for take away. Go inside and see what the queue is like for a table. It can sometimes be fairly short.
I would expect a taxi to the Castelo to be eight or nine euro and it is less than a thirty minute drive. You might start with the Tower, call in at the Discoveries Monument as you make your way to Jeronimos and finish with the Monastery visit (and the Fabrica Pastéis de Belém if you include that). You will find it easier to pick up a cab from there than from the Tower.
At the Castelo you might not bother with paying the small entrance fee and going inside. There are great views but not a whole lot else. The little museum is a bit dull. Without going in it is still a nice place to visit, you can have a bit of a wander in the streets inside the walls and take in the buzz. Do find Miradouro de Santa Luzia
the views are spectacular and the outdoor cafe/restaurant is good as long as you don't get impatient should service be slow. If you are there at a meal time try their cataplana - it is a bargain price, will feed a family and is not at all bad.
Thank you for your replies.Yes from what I have been reading the castle isn't worth going in, but want to see the great views there.Also I agree with you both I was already thinking about getting a taxi, don't fancy risking the packed trams with pickpockets.
<<Don't bother going into the Tower of Belem>>
Yes, yes and yes! We lost 90 minutes to get inside and there is nothing there! It is beautiful from the outside though.
Good plan, Richard!
Yes, I think so, however i do advise you to be early in mosteiros dos Jerónimos because normally there is a big queue. Transport wise, you should use the taxi.
I'm in Lisbon right now. I visited Castelo today. Unfortunately I'm not impressed with it.
Sorry to hear that, the castle is a old ruin, i think is very beautiful and has some amazing views. You don't have that kind of stuff in the states. The castle is older than anything in north america, it was used by the Romans, Moors and Christians. It was badly damage by the big earthquake. It's a castle not a palace.
Luis, it has nothing to do with what we have or do not have in North America. Fumri2000 is entitled to his/her own opinion. Personally, I was not stunned by the Castelo São Jorge as well and liked the Moorish Castle in Sintra much better. To each his own...
Trust me, we have enough in North America to entertain millions of visitors from Europe who come to the US and Canada every year. It does not matter how old the history is; it does matter what kind of history it is.
Yes i understand, it´s your opinion and i respect that. What i'm saying is that the history of the place is amazing, it predates Christ and it's very relevant to the history of Portugal which has more than 1000 thousands years. USA doesn't even come close to that, right
The bottom line, really, about anything "historical", regardless of age or location, is whether or not you can "feel" that history in the place. For me at least. It's not about what's on the attraction paperwork.
I too am not especially impressed with the Lisboa Castelo - I've been twice. The first time about 10 years ago (when it was free) - most interesting was an audio-visual exhibition about the earthquake, and the views - we were practically the only people there, which helped get a sense of the place. The second time was much more recently - surrounded by people, none of whom seemed to realise how loudly they were speaking, drinks sellers touting at me wherever I went, and forever avoiding selfie-sticks - none of this helps in trying to imagine the place in a time long-gone.
There are, I think, better castles (a lot) in Portugal, even more the world over - some more ruined, some less ruined, but many imbued with a palpable sense of what has come before.