I have got a playground environment and I would like to hide it from the people in the team for internal testing purposes.
When you create a "Team" in Octopus Configuration in the web portal, you can assign environments to that team.
This allows you to grant access to a specific list of environments and the others are effectively invisible, for example on the Dashboard, for the users of that "Team" (a team in Octopus is basically a permission group).