At 9 am, there was already a long queue at the entrance. Fortunately, we joined a skip-the-line tour, allowing us direct entry and saving a lot of time. Descending into the Basilica Cistern was truly breathtaking; I never imagined such a massive underground reservoir, built 1500 years ago, could be so well-preserved to this day. After the guide's explanation, we were free to explore at our leisure, with no time limit, allowing us to meticulously appreciate every column and corridor, every detail. This experience was fantastic, and I highly recommend it; everyone visiting Istanbul should come and see this.