The Cosmopolitan of Las Vegas has many little spaces that lead to wonderful new spots. One leads to a secret pizza place, one (we won't say which) takes you to an employees-only area that you can apparently stroll right into and act like you totally belong there, and another is the entrance to the megaclub known as Marquee. You many have seen the people lining up on the second floor of The Cosmopolitan, but if you've never been past the velvet ropes and up the elevator then you can't understand what they're all so willing to stand in that line for.The main room at Marquee is a classic club for which Vegas can be proud, complete with the showroom appeal of a Vegas lounge and the bumping badassery that makes Vegas clubs stand out from the grit of L.A. or the glam of New York. This is where you start your night, it might be where you end it too if you're still partying by the time you make your way back in, and it's where you remember why you come to a nightclub -- to dance beneath a disco ball to music that never takes a break. But that's just the main room. Every club has a main room. That's what makes them clubs. Marquee is much more than just a main attraction or a one-room wonder. It's as comprehensively complex as The Cosmopolitan itself.The Library is a warmer space than even the outdoor pool in the summer. The hues and ambiance change from sexy party club to sexy sit in a chair and discuss the politics of dancing (the song from the '80s not the actual politics) club. It's probably not the lounge you'll go to when you want a relaxing night and only a relaxing night. But if you want a respite from the dance floor and a chance to actually speak to that person who's been grinding on your thigh for the last hour, this is the spot. But that doesn't mean Marquee doesn't offer a happy middle.Enter the Boombox. Yes, it's true that many people who enter Marquee are too young to know what a boombox is. But they can still experience what it's like to be surrounded by music in a space so intimate you feel like you're holding it on your shoulder and walking down the sidewalk forcing everyone to be in on your beat. The Boombox features a 360-degree bar and VIP tables around an earthy dance floor. The tables in the back and side even have a view of the Strip, when the curtains are actually open. For everyone else who couldn't get in on the VIP service, there's an outdoor balcony that's just wide enough to sneak past a smoker and sit in a small lounge space. It only overlooks Harmon Avenue, but it's still fresh air. And in the middle of a night of hard partying, fresh air is a very good thing.None of that has even scratched the sunny, chlorinated surface of the outdoor space that becomes Marquee Dayclub, but we've got another page for that. In the months that it's open, that space pulls the whole of Marquee together to create a nightlife establishment far greater than even the marvelous second floor of The Cosmopolitan would imply. Some clubs are one-offs. Some are only good for afterhours or pre-gaming. But Marquee is an all-nighter. Start here. End here. And have a lot of fun in between. One of the best parts is, even if you do somehow get bored at Marquee, you're already in The Cosmopolitan so you won't have to walk far to find a good drink.