You do it on your own, but there are a group of them that are considered the "Bourbon Trail" and you get a "passport" that can be marked off at each one. If you get them all, you get an exclusive T-shirt or something I think.
The ones on the trail are (according to Wikipedia):
-Angel's Envy Distillery in Louisville
-Bulleit Frontier Whiskey Experience at the Stitzel-Weller Distillery in Louisville
-Evan Williams Bourbon Experience in Louisville
-Four Roses Distillery in Lawrenceburg
-Heaven Hill's visitor's center in Bardstown
-Jim Beam Distillery in Clermont
-Maker's Mark Distillery in Loretto
-Lexington Brewing and Distilling Company in Lexington
-Wild Turkey Distillery in Lawrenceburg
-Woodford Reserve Distillery near Versailles
For some reason I think they might have another, but I can't get their website to work on my phone right.
Of what I've been to so far, Makers and Woodford are my favorites. Makers is #1, like I said before absolutely beautiful property it sits on, good tour, and you can pay to dip your own bottle (which I gladly did!). Woodford is a close second, the distillery has a very upscale feel and the tour was very informative. Pretty much all of them have tastings at the end, but at Woodford the guide actually TAUGHT us how to taste bourbon which is what got me into it more.
Four Roses wasn't terrible, but the tour wasn't as cool IMO and I'm not a fan of their bourbon. Architecture was cool though. Wild Turkey I didn't actually get to go on the tours since their tour bus was broken down, but the gift shop was nice. Woodford and Makers definitely had a more upscale and classy feel, IMO.
Buffalo Trace is also worth a stop even though they aren't part of the trail. You don't get to see as much but it's very informative. To be fair, you can make reservations and do a "hard hat" tour where you get to see more, but they weren't doing those when we went because they were in a shut-down period so can't comment on that. The cool thing with Buffalo Trace is their tours are free.