Apple's second "spaceship" campus is scheduled to be completed in late 2016, giving the company just 12 months to wrap up construction to stay on schedule. Apple's construction crews have been hard at work over the past few months, making a lot of headway on the main ring-shaped building, the underground auditorium, and the parking structures.

Drone pilot Duncan Sinfield today shared another monthly campus update video with MacRumors, giving a close-up look at how construction has progressed since November.

Four levels of the main ring-shaped building have been completed, bringing Steve Jobs' original vision of the campus to life. With the walls in place, the special curved glass windows that will encircle the building will likely be going up soon.

This month's video also gives a clear look at the underground auditorium Apple is building, where it will host events to show off new products. Also depicted is the Tantau development, a set of additional buildings that will serve as research and development facilities.

When it's finished, the second Apple campus will feature the 2.8 million square foot ring-shaped main building, several parking structures, a 100,000 square foot fitness center, a 120,000 square foot auditorium, and a dedicated visitor's center with an observation deck, cafe, and Apple Store.