How do passengers make it to this point of the airport? By underground?
They are specially designed apron jet bridges. It looks like the normal gates but required to transfer passenger by bus.
A model shows how it runs (credit) :
This type of terminals are called "Satellite Terminals". Passengers are usually processed in a central building while aircraft are parked in remote docks. The satellite buildings are connected with the central building (if any) through tunnels or any kind or collective transportation (e.g. bus).
These terminals have a wide range of advantages and disadvantages when compared with more frequent types of terminals.
- Suitable for high traffic airports and hubs with a large number of connecting flights.
- Easiness for the aircraft to maneuver on ground.
- Easy separation of passengers flows (e.g. international pax, national pax, regional pax).
- High investment and maintenance of transportation services.
- Acces congestion at peak-times.
- Early check-in.
Munich (MUC) or Madrid (MAD) are some of the airports that have implemented this system.
The photo you show seems like a very special kind of satellite terminal with multiple remote "gates" and are probably managed by a bus that travels through the road connecting all of them.