I don't remember much about it. Animated, futuristic, space fantasy.

The main character's a blonde girl. At one point, she gets swallowed by quicksand. Near the end, she's riding a giant "alien," a very large creature, big like a stadium, with yellow, glowing tentacles at the bottom.

Very epic. I must know. Help!

Is it "Nausicaa, of valley of the wind" by Hayao Miyazaki?

All right! That looks like the one. Thanks, Hippiefeet. I was thinking no one here knew. Finally.

I watched that movie online for free. I just did a Google search for it.