Hm. I'm not sure which key you're going for last so here's both of them:

To get the one in the square room with only the lone Jupiter statue (that says "keep walking and you'll find the key")in the middle - nothing else in the room - do what she says - walk over EVERY square of space in that room. Eventually you'll find an invisible object stops you from walking - that's the key. (I found it on the upper right part of the room but I don't know if it's randomised).

To get the one in the room with the Jupiter statue and the two Jupiter symbol swamp-patches, look around the right side of the right-hand symbol. It's invisible again, but you can't walk over it so you'll find it easy enough. It's right by the symbol so walk close to it.