Depends what you mean by the best ...... but the largest is Canyon Ranch at The Venetian.


The largest fitness facility on the Las Vegas Strip includes:

Complete, leading-edge cardio, weight-training and Indoor Cycling gyms
40-foot rock-climbing wall
A wide array of daily classes
Personal training

for more info check out their web site

The Bellegio's gym is the best Ive seen though I havent seen them all obviously. I actually felt happy about paying the fee to use it (not a typical thought for me-lol)
It has pretty much everything any private gym would have though smaller than say Ballys, its' a hotel for God's sake.
Dont think you would go wrong with either The Venetian's or Bellegios'.

That's good info.  One thing that has disappointed me about some of the hotels is that they don't keep the fitness areas open late.

Any you know of that keep them open 24 hours?

No I don't think any hotels keep the fitness area open 24 hours ...........after all they do want you gambling ,not working out

That is also why they close the pool areas early.

Maybe at a non gaming hotel you can get access to a fitness center 24 hours........but they just usually have a small room with one treadmill and a few weight machines......nothing to brag about.

but many 24 hour fitness locations across the valley. If your a member you can go there 24/7

in the past.  I'm usually in town for about a week.  And what I find has worked best for me is to get a 7 day membership to 24 Hour Fitness for 50 bucks.  That's very reasonable, they are open 24/7 and have several locations not far from the strip.  Even if you are just there for a weekend, the 50 is not that bad, compared to the 20-50 a day the hotels charge.