VENICE — When “Sun & Sea (Marina)” won this year’s Golden Lion, the top prize of the Venice Biennale, it was measured against works of predominantly visual art.

But “Sun & Sea” is an opera — an excellent one that, in the event of a similar contest among new operas from around the world, could still come out on top. Within a single hour of dangerously gentle melodies, it manages to animate a panoramic cast of characters whose stories coalesce into a portrait of an apocalyptic climate crisis that goes down as easily as a trip to the beach.

What’s less easy, however, is getting in to see it. The opera, Lithuania’s contribution to the Biennale, which is on view here through Oct. 31, may be a prizewinning hit. But it’s also expensive to mount, and was only recently made available two days a week , instead of one, after a passionate fund-raising effort. Even with added showings, the line to enter is long, and slow-moving.