A towel, it says, is about the most massively useful thing an interstellar hitchhiker can have.
Douglas Adams
Who: Geocachers and Hoopy Froods
What: An event about towels
Where: The picnic shelter at Lake Meridian Park
14800 SE 272nd St, Kent, WA 98030
When: 6:00pm - 7:00pm
Bring: A towel
Why: It's Towel Day!
Towel Day is a tribute to British author Douglas Adams (1952-2011). Adams was a well known author, scriptwriter, essayist, humorist, satirist and dramatist. This special day was established by his very loyal fans, and is popular in The United Kingdom. Towel Day was created to honor Adams, and as a celebration of his many works.
To understand the meaning of Towel Day, one must know The Hitchhiker's Guide to the Galaxy, an original radio series comedy aired in England. The towel was introduced in the radio series in 1978. A follow-up book explained the importance and usefulness of towels to hitchhikers.
You can celebrate Towel Day by carrying a towel with you. If you want to, you can further enjoy this day, by reading Adams' book: The Hitchhiker's Guide to the Galaxy. Or better yet, attend this event. 
Origin of National Towel Day:
Fans first celebrated this day on May 25, 2001, two weeks after Adams' death (May 11, 2001).
This special day originated in the United Kingdom. We have not found any proclamations from Parliament or Government leaders establishing this as a true "national" day. Nor, has the Queen of England made any proclamations on this that we are aware of.
Event Activities:
Pimp my towel
- Decorate your towel to be the coolest and fanciest towel anyone has ever seen, and bring it to the event.
- Bejewel it! Embroider it! Tie-dye it! Cover it with gewgaws! Hang it from a drone and make it fly! The only limit is your imagination.
Towel snapping at targets
- How good are you at snapping a wet towel at things? This will be your opportunity to show your superpowers!
- You can't say you don't know how: https://www.wikihow.com/Snap-a-Towel
- Please resist the temptation to snap your fellow cachers.
Towel Fashion Show
- Adorn yourself with towels.
- What cool outfit can you make with towels? Togas, dresses, kilts, capes - use your imagination!
- Strut your stuff
Prizes will be awarded for the most pimped out towel, most accurate towel snapping, and best towel fashion!
That's right, you can take a dip in Lake Meridian and dry off with your towel! 
Towel Day is celebrated every 25th of May as a tribute by fans of the late author Douglas Adams. On this day, fans carry a towel with them to demonstrate their love for the books and the author. Or maybe just because they're crazy.