Smiling back, Castiel swims downward with Dean.

At first, they pass small fish, but as they swim lower, they start to see strange deep-water fish and then things that Castiel knows for a fact aren't real at all. Eventually they pass a large-breasted mermaid and Castiel rolls his eyes at Dean.

That's what he spots a rusty old crate and he starts to steer them towards it.