Hole under transmission block?

Yesterday, I checked my truck (2003 ford expedition) and I noticed there was a large hole near, what I thought, was the transmission. It seemed like there should be a plug there, as it was around 2 inches diameter. I looked into the hole and there appeared to be a blue belt and then a gear with teeth. There was also something leaking out which was dark brown, which I thought was just oil. I have had my transmission changed twice in the past, so I was just wondering if it's something I should be concerned about. I'm going to be driving 5-8 hours this weekend so I want to make sure there's nothing wrong with the transmission.

An open hole in the trans is NOT a good thing! Get to a shop and have them replace the plug, if Auto Zone doesn't have one for you.

Your not looking at the transmission your looking at the transfer case and it will not last driving five to eight hours. There's nothing I know of with a plug the size you say the hole is and I'm sure your not the one going to fix it so take it to the shop of your choice.

You most likely will not be driving it this weekend! If you are unwise enough to try you may not get very far.