Life is short and then you die… and discover giant two-headed sandworms lurking in parallel dimensions outside your door.
The dead just can't catch a break.
Adam and Barbara figure out as soon as they get home that they're not able to leave their house without being transported to the planet of the sandworms. It's a vast sandy landscape where horrifyingly huge worms snake in and out of the ground. They have two heads and alarmingly sharp teeth.
Betelgeuse hints early on in the movie that sandworms are his Achilles heel. He gets upset when reading an article about them in the newspaper and then tells Adam and Barbara how much he hates them:
BEETLEJUICE: We're like peas in a pod, the three of us. Let's face it—you want somebody out of the house, I want to get somebody out of your house. Look! You've been to Saturn? Hey, I've been to Saturn! Whoa. Sandworms. You hate 'em, right? I hate 'em myself.
When Barbara, at the end of the movie, rides a sandworm into the house to swallow Betelgeuse, it represents her triumph over… well, not over death, but over her cluelessness about the afterlife. She's made it work for her. This gentle sweetheart faces her worst fears and kicks some sleazebag demon butt.