What to do with the bedroom fireplace?

[Garbes]

Hi, I'm new to the forum. We moved into a Victorian house around 7 months ago and we are working through each room.

We want to install a decorative only Victorian fireplace and Pictures 1 & 2 is how is started.

Want I wanted to do was plaster the chimney breast, remove the current hearth tiles and replace with more decorative hearth tiles. Ensure the base inside the chimney breast is all structurally sound....it was going ok until this part.

After removing all the tiles I uncovered rubble with I thought would be a simple case of clearing out. But this just seems to keep going and going and the hole is getting deeper, as shown in Pictures 3 , 4 with the rubble taken from the hole in Picture 5. Below this bedroom is the kitchen with this chimney breast if this

My question is, what should I with this hole. I would like to fill it and either cement, or put some short floorboards in situ. But I'm looking for advice on how I
should proceed please?

Picture 6 shows the chimney breast below, which is in the kitchen.

 

[mardinor]

It looks like the rubble infill to the old chimney breast. Not sure what the problem is? Chuck the rubble back, concrete on top to level, then add your decorative fireplace.

 

[Garbes]

Thank you. I just wanted to check that this was the correct thing to do.

 

[Craig89]

There is a dead space created as the flue from the ground floor fireplace sweeps over to the right to make way for the bedroom fireplace. Perfectly normal. Throw all the rubble back in, compact it and tile over it