With adventure meaning different things to different people why not plan an event of small project where members and / or their groups can challenge themselves in some way?
Perhaps you can create a sense of challenge by:
Investigating a new habitat – survey a new site, coastal or inland, complete an OPAL survey
Go on a quest – make a community garden, go geo caching, orienteering, scavenger hunt, bear hunt!
Have an adventure – go on a rescue mission, spend a day in a wild place, solve a problem.
Explore - a local green space, go where the wild things are!
Network groups can apply for the small and special grants via the website as usual or if the group wish to amalgamate both grants just fill in one of the forms with details of your plans.