Old Airfield
From Kerbal Space Program Wiki
The Island Kerbal Space Center is a landing strip, hanger and, command center located on the largest of the string of islands east of the main Kerbal Space Center. The landing strip has a grass-like texture to make the Space Center harder to find from the air.
Spoiler: Easter egg
In the far right hangar, there are some old rusty parts lying around. These are the old models of the Command Pod Mk1, FL-T400 Fuel Tank and the LV-T30 Liquid Fuel Engine. Note that the command pod's scale is incorrect; it now appears to have a large radial size on the bottom, although it had a small one while still available as a part.