To inspire your employees to try something new and challenging outside their normal work environment, why not assign them a task or two, every now and then. Here are some ideas:
Present a proposal to management
Organise a company social lunch
Write a media/press release
Install a new system
Create a team to work on a new assignment
Plan a convention or conference
Supervise a team
Handle negotiations with a customer
Represent the company at the careers expo or trade show
Make a speech for the organisation
Go on a business trip to another country
Go to a campus to recruit
Work for a short time in another unit of the organisation
Manage an office renovation project
Design office layout
Work on a project with a tight deadline
Manage the visit of a corporate official or VIP
Launch a new product/service
Or why not give them the opportunity to do some training to enhance their skills?