We had enough time in Lisbon to head over to the aquarium. I had read in many TripAdvisor reports that the entry lines were about 2 hours - with a timed ticket or without. I had also read that there is an afternoon clear out of the backlog. So we timed our entry for 3pm. No lines at all - either for pre-timed entry or walk-up ticket purchase. It’s a pretty great aquarium with the best close-up penguin exhibit I’ve come across.
We made the decision to walk from our Baixa area hotel all the way over to the aquarium. It took us about 90 minutes and was interesting but did not take us through the most charming areas of Lisbon. We took an Uber back and laughed at ourselves the entire time - the Uber cost 7 Euros and took less than 10 minutes;)