It has the original engineering drawings of many of the places the canal was proposed and surveyed and was going to be built before Panama was finalized for practicality and political reasons.

To quote my own blog from when I was there:

> The number one attraction in town is obviously The Canal and before visiting I make a stop at the museum in Casco Viejo which is amazing considering the tiny $2 admission price. My engineering background means I’m fascinated by the surveying work that was undertaken before construction began. One map in particular shows proposed routes through Tehuantepec in Mexico, through lake Nicaragua, through a couple of different places in Panama and finally one using a river mostly in modern-day Colombia. The decision didn’t actually come down to the “shortest” distance to dig as you might think, but primarily on how the mountain range through Central America would be dealt with. The final location chosen meant it was possible to create a huge in-land lake and use locks to elevate the ships 28 meters to that level.

Really, really fascinating. I went back for a second day.

(I assume you're talking about https://en.wikipedia.org/wiki/Nicaragua_Canal )