The Royal Mail is set to open the doors of its Hemel Hempstead centre to the public on April 1.
The open day, from 11am to 3pm, will raise money for Prostate Cancer UK .
Tours of the site at Maylands Gateway plus machiery displays will give a behind-the-scenes peek at the postal system.
Youngsters will be able to take part in mini quad-bike racing and play post-themed games. A raffle and refreshments will also be available.
Admission will be £2 for adults, and £1 for children under 16.