I have lifted a carpet in the front room and found this scenario. Not sure what is going on here or what to do. The tiles are flush with the piece of concrete. Thank you
Looks to me as if the fireplace once had some sort of 'surround' to it - quite sensible if you think about it, to prevent anything falling from the fire grate landing beyond the tiles.
What to do depends on what you want to achieve. Is the fireplace intended to be used? Is the floor going to be re-carpeted or is the intention to have bare boards?
FWIW, we had a similar scenario in a bedroom and I made a simple oak surround as a border between the tiles and the floor, in our case carpeted but it would have worked with bare boards.