What's this hole doing in my engine?!

[impboy]

I got all ambitious and decided to change the spark plugs on my '01 Box. As I was under the car cursing how tight everything is and taking forever to get the allen head bolts off the coil, I noticed this hole on the driver's side of the engine. From a distance it looked threaded until I reached way up in there and felt around and could feel that it was smooth.

I stick my finger in there and could feel some kind of metal but what, I don't know. All I know is that this doesn't look right and I'm guessing some kind of plug is missing. Please look at the pics and let me know what it is I'm looking at and any advice about fixing it if it needs it.

Thanks in advance!
evan