Definitely a good place to go if you're just escaping Marquee. And I know you just got out from the horrendous stairway, so now you're suddenly starving. The sweet smell of cheese and tomato sauce isn't helping, just follow your nose and it will lead you to the secret hallway to the place they call Secret Pizza.
If you found the secret because the line is a mile long, sorry it's going to feel like a century to get in. I would avoid it between 12-2am, but they close at 5, so get your timing right! You can always call for a whole pie. The prices are pretty cheap for Vegas.
For those not staying at Cosmo, it's great because there is plenty of seating outside.