Mount Rainier, Washington

I was there for two days last summer. The Paradise section is really pretty when the wildflowers are blooming. Lots of good hiking trails around there. Try to get up to Panorama Point. Also stop and visit Christine Falls, Reflection Lake and Grove of the Patriarchs

That's assuming you come in from the South Entrance. I've heard the northern and eastern sides are nice too but I didn't go over there (it's not easy to get around different sides once you are there).

Not sure what you will do as far as bachelor party stuff. Not much going on in that area besides hiking, etc.