Rating this show a 2 star just for the very limited entertainment value, like watching a train wreck you just can't help not turning away from.
First couple episodes I thought it was all possible, then it started to nose dive, like drilling a hole above the "box" but never use it except to drop a chain into, can't take the rock samples using the hole? Then there is a matter of trying to drag a 500 year old wood box tied with 500 year old rope that's all been under water for 500 years out of a cavern that was stated to tight and narrow for a diver with scuba gear on to get through?
The show escalated everything to unbelievable and made up. The last episode split into 2 was the final straw(s) for me, wearing sealed suits and they're worried about a toxic gas and the suits were for protection from radiation, might protect them from internal contamination but radiation is energy and the suit does nothing about that. I've seen a lot of mining shows and have never seen a nice, level sandy floor they were walking on with no debris anywhere.... Advice to Discovery, try and make your sets a little more realistic, your "experts" a little more knowledgeable and put a little more "common sense" into the story line