Does anyone know the significance of the giant sized objects in the imperial palace basemant?

I believe they are the products of experiments, and also, try putting all your questions in one thread

If I remember right from a thread years ago on this, it's a tribute to another video game -- Prince of Persia or one of the Thief games, I think.

The Glass of Time you have to activate ( a giant hourglass) might be a reference to the Sands of Time from the ps2 Prince of Persia games. Or, it could be a reference to the original Prince of Persia games, where the snads of time were a mundane giant hourglass.

I thought they once belonged to a Giant.

No explanation is ever given. In fact, when your told to activate the Glass of TIme, The Grey Fox doesn't even know what it looks like. No one explains it. Though a giant would be the only thing that could carry the giant club that's there.

That's why I assume it's furniture that belonged to a giant, or maybe a demigod from a previous kalpa, or earlier in the Mythic Dawn era.

We know for a fact giants existed and still do. They were in Daggerfall. They will be in Skyrim. One of them was in Bloodmoon. They appear in many legends and books including the suit of armor from Castle Xyr.