First, I ask you to think about all of the thermal features in the Old Faithful Area. Then, think about the incredible size of the Inn. Lastly, think about the Inn's close proximity to the Myriad Group (For those who don't know the Myriad Group - it is the OFF LIMITS thermal area to your right just before you get to the Lower Hamilton Store). With all of this put together you just have to say to yourself, "There has to be thermal features under that Inn!!!" You would be right.
During the construction of the facilities and roads at Old Faithful, several "in the way" thermal features were covered. In some cases, the features just ceased to exist. In others, the energy found a new outlet. Yet some also found there way back into existence by persevering over the construction of man (prime example of all three: The springs along the paved path near Riverside Geyser)
The Inn is no exeption to this. While I have no knowledge of how many were covered, I know this for sure - there is at least one feature under the Inn that is still active!! Now, don't be alarmed, it is not dangerous - it is not a geyser, just a hot spring (or, Dave M. believes Marie Wolf said it was a mud pot), and it is causing no problems. But before I get too far ahead of myself, let me explain. While adding the West Wing (I believe that the wing closest to the Lower Hamilton Store is the West Wing. It does face west, but it has been years since I have stayed in the Inn so as to actually pay attention to what the wings are called) onto the Inn at least one somewhat active thermal feature stood in their way. In order to solve this problem, they put a cement plug in it and continued to build. The West Wing was completed and everyone forgot about this spring. That was until steam started to leak out from around the plug and fill the room that sits above the old spring. Interestingly enough, if I recall correctly, the room above the spring is a boiler room!! So where exactly is this room, you ask. If you leave the Inn lobby going past the gift shop (First hall way on your right as you enter the Inn) you will eventually come to a somewhat cylindrical room with a stairway, telephones, and access to the outdoors. The room and the spring sit underneath this in the very foundation of the Inn.
Kinda spooky isn't it? Gives me the chills whenever I am in that room. Reminds me of ghosts!!