Basilica Cisteren

It says there are some extra light shows at night. Check your dates because it is temporarily closed, but they say there is a different cistern you can tour instead (i didn’t see that one).
https://yerebatan.com/en/
https://cisternoftheodosius.com/

We thought the Basilica Cistern was pricey. It was interesting to visit, and we enjoyed the history and structure and secondarily the art. While we liked it, it certainly would be lower on the list than the mosques, Topaki Palace, etc. We visited during the day. We would not have paid the additional cost to go at night.

I went to the Theodosius cistern because the Basilica was closed when I was there. It has a light show all the time I believe. It was interesting but not a highlight of my Istanbul time.

There is no need to go Basilica Cistern at night. Its underground and has the same lightning all the time.

I wouldn't pay to go at night. I visited it during the day and didn't need a light show to enjoy it.

Thanks everyone!

I really liked it, it was fascinating and more interesting to me than the mosques. I have no interest in a light show as that, to me, detracts from the architectural and historical aspects of it so I would advocate visiting during the day unless you're particularly interested in a light show.

I went during the daytime alone and about a year later with friends at night (timing issue). There was no noticeable difference at all.

We went in the afternoon after the blue Mosque and the haga Sophia. I found the mosques (and the queuing up process) to be crowded and over stimulating. The Cistern was the quiet palate cleaner that made istanbul tolerable for me. YMMV
(I then skipped the spice market)