Very easy to get lost for sure, and outside is all jacked up right now with the race track construction too.

Here's a map. There are at least 3 ways to get into Aria from the street -- one from the Vdara side, one from the drive that comes up from the Strip (see red arrow), and another walkway that comes up where the "Big Edge" statue is. The Vdara and Aria entrances are both a fair bit above Harmon Avenue ground level. You can also enter from the Crystals shopping mall which is probably the easiest way to do it, just go into the mall from the street, follow signs for Aria, and it will put you right in the Aria check-in lobby, where you'll easily see 1850.