Don't you need the key to activate the elevator? The keyhole is at the end of the corridor with the elevator.
To enter the desert tomb you need something else than a key, but that will be revealed further on in Skull Castle.
About swimming against the current: today I saw a post about 'skiing': running on water with your head held high (: looking halfway up). That won't help you here, because you need to go under water, but wouldn't it work in dragonspire?
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