If you have never been to
Luray Caverns (in Luray Virginia), you should go. Especially if you have kids (bring them along of course). Luray Caverns is one of the most impressive underground cave systems in the country, and certainly the best one within a days drive of Maryland. It is less than two hours away from Bethesda so you can easily make it a day trip.
It isn't the biggest cave system, actually, it is fairly small. It's claim to fame is the plethora of impressive stalactites, stalagmites, and flowstone. They have guided tours that go through the cave following a paved path that is suitable for both wheel chairs and strollers. The tour itself takes about an hour, but there are other things to do on the property such as seeing the Luray valley museum or the antique car museum. The car exhibit is surprisingly good, the pack a large number of examples of early automobiles in the exhibit and it is well worth the time to walk through it.
One of the more unusual formations is called "fried eggs" because it resembles two sunny-side up eggs. They say that the centers used to be yellow like egg yolks but the color wore off from people rubbing them.
This isn't a place you go back to year after year. It doesn't change much. However, going there every 20 years or so is well worth the effort. If you have already been there, you should consider going to
Skyline Caverns too. I don't think it is quite as awe inspiring, however, it does have some types of rock formations that Luray doesn't have, so if you like Luray, you'll probably like skyline too. I have some more
pictures of Luray Caverns if you want to see them.
