Walk the floor of the assembly building and the hangar in first person, at a kerbal's height: among the ground crew, under the rocket on its clamps, out through the great door. And a car for the ground crew to drive about the space centre: an airport baggage tug.
For Kerbal Space Program 1.12.x. Needs Keystone, a separate download (on SpaceDock): this mod does not load without it.
Copy the OnFoot folder from the download into your KSP's GameData, beside Keystone.
The same page has the walking and running speeds, the eye height, the mouse and the field of view.
Windows 11 (Direct3D 11) and Mac: tried. Linux: never run.
More: the long description (everything in full, and what was tried on each system) and the rest of the wiki.
CC BY 4.0: use it, change it and pass it on as you like, as long as you credit Ishiaki and link back here.
Raw stats are from the beginning of time until now. Each follower and download entry represents one hour of data. Uneventful hours are omitted.