John Hancock tower is visible from just about anywhere in Boston. But let’s look at five things you didn’t know about the Boston’s tallest building.

1. Trouble From The Start The John Hancock Tower ran into trouble very early on.During the excavation of the tower’s foundation, temporary retaining walls were erected to create space in which to build. The walls wound up warping though, giving way to the clay and mud they were meant to hold back. The inward bend of the retaining walls damaging utility lines, the sidewalk pavement and some nearby buildings. Hancock wound up having to foot the bill for repairs.

2. Motion Sickness Early on, occupants of upper floors often suffered from motion sickness. The building would sway too fast for comfort in regular wind conditions, moving a few inches forward and back and at the same time, twisting. Engineers would go on to fix the issue by installing something called a “Tuned Mass Damper,” which is also used for the Citicorp Tower in New York.

3. Windows Falling Perhaps the most dangerous flaw on the John Hancock Tower was with the windows. Entire 4′ x 11′, 500-lb windows were detaching and crashing down to the sidewalks hundreds of feet below. Police had to close off surrounding streets whenever winds reached 45 mph. After a huge amount of testing, and a period when the building was covered by sheets of plywood, the problem was diagnosed. The issue turned out to be air space between the two layers of glass. All of the windows were replaced with single sheets of tempered glass.

4. Observation Tower The observatory atop the John Hancock Tower was once a very popular tourist destination. However, it was closed following the 9/11 terrorist attacks in 2001. It has since been used sparingly, mostly for private functions. The building’s owners have expressed intent to replace it with more office space. City officials argue however, that the observation deck was part of the deal when the city granted permits for the tower to be built. The city hasn’t been able to find evidence of that alleged agreement, though

5. What’s It Worth?

The Hancock Tower has been bought and sold four times in the past decade. In 2003, Hancock sold the tower and a nearby garage for about $639 million as part of a larger deal. Three years later, the same building and garage sold for more than double – $1.35 billion – as part of a larger deal. The housing bust sent the tower into foreclosure, where it was bought for $660.6 million in 2009. Those owners turned it around 18 months later for $930 million.

Bobby Driscoll is a student at Franklin Pierce University. He is currently interning at CBS Boston for the Summer of 2013.