This image comes from a site about aircraft tractors:
What is the type? Why the large pipes at the flight deck windows? What is this place? Why is this plane here?
In most commercial aircraft, the cockpit windows are the most easily opened/removed.
Why the windows typically open is a topic for another question, but mostly it is for the crew to be able to communicate with the ground personnel and for rapid evacuation.
Some older aircraft like the 707 in the original post are used primarily as training devices. The aircraft in the original post is a Boeing 707 in Germany used for evacuation training. The most likely explanation is that they put in portable air conditioning units to be able to cool the cabin while they filled it with people. The vents are angled down so that water does not enter the air conditioning system.
Specifically regarding the aircraft in the post, this is a Boeing 707 located at the Tegel Airport in Berlin, Germany. It has a lot of history being an aircraft that was hijacked and then later smuggled back into Germany in the night by an American crew as a gift from Boeing to celebrate the city's 750th birthday.