Originally Posted by Carbonfiberboy

I associate fitness for rando with "the ability to repeat." IOW, you'll always be doing a lot of climbing, so you want to build the ability to do climb after climb, recovering on the descents or flats which join them. I've found the quickest way to do this is to simply hit lactate threshold on every climb up to 1000', on training rides up to about 80 miles, figuring about 50' of climbing per mile or so. If you can do that, you can ride however far. For just a 200k, probably 60 miles of that is far enough.