Starting in late April/early May, you can get May Day Tickets to visit a special island.
May Day Island
In late April/early May, you can visit May Day Island by going to your airport. Your belongings will stay behind at the airport.
May Day Island is a maze that you have to find your way through. If you are stuck, you can use the Rescue Service app on your NookPhone to start over. The Rescue Service costs 100 Nook Miles per rescue.
You can talk to Wilbur if you need hints.
Navigating the Maze
During the maze, you will find a shovel, which you can use to dig up shrubs. You can also find fruit, which you can eat, allowing you to use the shovel to break rocks and dig up trees that are in your way.
You can get tree branches by shaking trees repeatedly. Depending on the maze, you may need the branches as a crafting material, so shake the trees to get branches just in case.
However, try not to eat the fruit if you don't have to. If you have extra fruit after reaching the end, you will be able to eat them to break the three rocks that block a set of bonus Bell Vouchers somewhere on the island. (If you don't have enough fruit at the end, you can pay 100 Nook Miles to use the Rescue Service to try again to get these extra Bell Vouchers before you leave.)
You can jump over square holes in the ground by trying to walk over them.
Be sure to pick up everything that you find on the ground in the maze. There is a DIY workbench in the maze, and you will be able to use the materials to build tools to help you get through the maze.
If you find a Worn Axe, you can use it to cut down one tree. The axe will break after cutting the tree, so choose carefully.
You may need to craft a Flimsy Axe, which you can use to craft an Axe. Be aware that the Flimsy Axe can't cut down trees. You should only use the Flimsy Axe as a crafting material to make the Axe, which can cut down trees.
When you reach the goal, there are some Bell Vouchers that you can reach by digging up shrubs. There is another set of Bell Vouchers that you can only reach if you have extra fruit.
Talk to Rover
Rover is at the end of the maze. Talk to him to get a gift, which you will get in the mail the next day.
Talk to Wilbur
Talk to Wilbur to leave the island. Rover's gift, and any Bell Vouchers that you found, will be mailed to your house.