If you want a breadth of grounded fantasy (IE takes place in our world but contains elements that don't really exist in our world) then I would recommend picking through Stephen King.
If you want to completely escape our world then I recommend the old Conan books or the modern Brandon Sanderson starting with Stormlight Archive.
You have received plenty of Sci Fi recommendations but I will add my own personal favorite (this is one novel in the series): https://en.wikipedia.org/wiki/In_Death_Ground
If you want fiction that is grounded in reality with little to no fantasy elements then the murder mystery genre has quite a few gems that are fun to try and guess the twist of when you are reading. Murder on the Orient Express is great if you havn't experienced the story yet.