While Disneyland Paris consists of two parks—Disneyland Park and Walt Disney Studios Park—it is entirely possible to see the "highlights" of both in a single day, though "seeing everything" is a stretch. Because the two parks are only a 2-minute walk apart, "park hopping" is incredibly easy. To succeed in one day, you should arrive at least 30 minutes before "Extra Magic Time" (if staying on-site) and prioritize Walt Disney Studios in the morning to experience high-demand rides like Ratatouille and the Avengers Campus before the crowds peak. You can then spend the afternoon and evening in the larger Disneyland Park for the classic castle vibes, Big Thunder Mountain, and the fireworks. Utilizing the Disney Premier Access (their paid skip-the-line service) is almost essential if you want to hit every major attraction during a one-day visit. While you might miss some smaller shows or walk-through exhibits, a well-planned itinerary starting early in the morning can definitely cover the most iconic and thrilling parts of the resort.