I have been reviewing the posted messages and noticed a lot of you have mentioned that a place not to miss visiting is the Cathedral (in Washington DC), especially the "Moonrock" window. What is the name of the Cathedral and where is it located?

You have reference to the Washington National Cathedral located in Washington Dc. I don't know the official address off hand, and the web site does not give one. If you drive northwest, up Massachusetts Avenue toward Wisconsin Avenue, you cannot miss it. The turn into the parking areas at one time was off of Wisconsin Avenue, after a right turn from Mass Ave onto Wisconsin, assuming you are going northwest.

Parking around there is scarce. You can get there with metro and bus.
The web site tells you how.

Taking the bus up Massachusetts Ave. to get there is interesting, as you pass numerous embassies. If you drive, look for parking in the surrounding neighborhood.

The cathedral is awesome, both inside and out. Don't miss the garden behind the stone wall.

I'm not usually a tour fan, but if you can get into a group tour, you won't regret it. They tell you many fascinating things about the Cathedral and take you down into places just walk-around visitors can't go.

The National Cathedral is a fabulous example of Gothic architecture, located on the highest hill in DC (near intersection of Mass. and Wisc. Aves NW) is worth a visit and taking the guided tour inside. However, if you have been to some of the great cathedrals of Europe, there might be other DC sites you would enjoy more.