I found the arch myself yesterday. I wonder if there are any other 'anomalies' on the Munar surface to be found?
There is

As for how to get to the Mun...
Fly up to about 10km then bank out towards the 90º mark on your compass. Then get up to 2kps in a nice orbit around kerbal (hopefully you are going around the axis. If not you will need to adjust it. Then wait for the mun to come over the horizon towards you and burn straight for it it. Your orbit should pull you down and away into it's orbital trajectory. Then open up your map with M and wait for your orbit to go out to the mun orbit. It should turn yellow when it calculates a mun capture.
Then try not to die...