A layer of insulation is laid down before the slab is poured. You can also see the grid of rebar which will give the slab more strength.
The poured slab in all it's glory. Radiant heating and a travertine stone tile floor will eventually be sitting on top of this.
The blue basin will be set in the poured pit on a bed and surround of sand.
And just because it was such a nice day out I took some shots from the back of the house. You can see the new gutter in the second picture. There will be a fake "extension" gutter to simulate the continuation of the leader.