Question

I am writing a book on a mysterious city which is fiction give ideas for that

Answer 1

Hey! Well, the most important thing in a mysterious book is darkness and the depth. Try to keep suspense in it.
You can start like -
"I just shifted here, the home's bit old, but nice. And alas! I just came in and the rain started off!"

Answer 2

Describe the city well. Like you can give it a dark look. And you don't like that place Cruz the vibes are not so good. Like the kind of situation in the wake me up video by Avicci. You can also include a male character who's quite mysterious and has got looks like Zayn Malik Cuz he looks quite mysterious. You can describe yourself as a quite curious person. And like as if the male character is involved in something and you're trying to get him.