If you have a Lisbon card in your pocket, you can use the free ride. Otherwise, it is much better to walk to the observation deck on foot. And this viewing room is not the best.
Long queues and a very long time to stand. In my opinion, you can find no less than other viewing platforms in Lisbon. In this case, you can simply take a taxi and arrive at the top point without wasting time.
I think it's not worth it to stand and wait for half an hour until the queue comes up and still pay 6 euros for it, it's expensive! A train ticket to Sintra costs 2.50 euros for 35 kilometers))) There are plenty of viewing platforms in Lisbon