How are the crowds in Lisbon in late Sept? It looks like summer is a mad house. I don’t like going to cities crowded with thousands of tourists. I visited Prague 2x, one in summer I hated and once in December that I loved. I love traveling Eastern Europe because of this reason. I understand there will be tourists anywhere I go but don’t want to go somewhere where it is wall to wall visitors.
By late September, the worst of the hordes are gone. But, with cruising becoming a bigger thing in Lisbon, you might want to check out the cruise schedule and plan your day trips on days when there are multiple cruise ships in port.
Even in the height of summer, there are areas with lots of congestion and those that are still relatively quiet.
When we were there in mid-October of last year, the lines to the Monastary in Belem were just as long as in the summer, and the city and Sintra seemed just as crowded. I've come to accept that crowds regardless of the season is now the "New Normal" almost everywhere in the EU.