There's a lot of issues you can bring up and explore with a lost city. I'm not sure from what you've provided here how many of them could work with your story. But everything I've read/seen has focused on things like:

-What happened to the people who built the city? How did it get abandoned/buried/lost to begin with?
-Discovering some form of technology or knowledge those people possessed which has since been lost.
-Exploring and explaining your world's culture and history
-Using the city as a means of explaining mythic events from your world's past (like...this is from back when this planet was part of a galactic empire/ruled by other powerful beings/from when WE had a galactic empire!)
-Following opposing parties who are both hunting for some ancient object of great value...the holy grail, the spear of destiny, etc.
-Exploring the city exposes the characters to some disease that had been contained/dormant within the city until they arrived.

There's a lot of options. I really like books and tv shows and movies that explore ancient, forgotten places. So if you want some recs, I can make a list.

But this might be more of an under-developed plot problem. If there isn't anything really *plot significant* about your lost city, then it's just a backdrop.