Online tickets to Galata Tower and Basiica Cistern

I’ve never purchased tickets in advance and never had any lines at either site.

If, by chance, you are going on the Best of Istanbul tour, you will get an Istanbul Museum Pass that will give you free entry to the Galata Tower. We visited twice, once before our tours and once during the Best of Istanbul tour.

You can buy your ticket online from the tourism website:
https://muze.gov.tr/urun-ekle?catalogNo=WEB-GLT03-01-008

For our first (pre-tour visit) we bought our ticket on arrival at the tower. On a Saturday at 12:30 in late May, my friend waited in the 15 minute ticket line while I waited in the hot-standing-in-the-sun 20 minute entry line, which you have to wait in, even with a ticket.

For our second visit, with our tour-provided Museum Pass, we ignored the long line for tickets and went straight to the entrance where there was one couple ahead of us.

There were significant lines at Basilica Cistern when we were there earlier this month, both times we walked by. We walked past a long line to go in with our guide on a Sunday morning, and saw a long line when we walked past the next day on our way to Topkapi Palace.

We did not go to Galata Tower so can't comment on lines there.