[Weasel9992]

That's a tough room. Not impossible, but tough. You'll need floor-to-ceiling trapping in all the corners you can manage (is that a sheetrocked column in the upper left?) and since it's such a small room, lots of trapping along that broad back wall as well. You didn't give the ceiling height and composition, so I'll assuming sheetrock@8'. You'll need lots more absorption here to avoid inevitable comb filtering from the short returns. That door on the left and the way the room kicks out on the right complicates the first reflection points.

Isolation will also be a big issue. I think the above poster is right...short of floating another room and adding lots of mass you'll bleed right through to at least the floors above. I'm not sure that's practical in a room this small.

I prefer to work with what you've got, so I don't often give this advice, but honestly, if I were you I'd try to find another room if there's any way. I imagine that space is at a premium in Athens, but it might be easier to find another place than to do everything you'd have to do to make this one work.

Good luck,
Frank