The mission starts with Agent 47 on the pier. Head towards the two guards standing outside the elevator. Make sure to hug the wall as you approach the elevator, otherwise you will be caught on the security camera. Enter the elevator and ride up to the party floor. Head past the waiter and around the balcony. Go past the spas (you'll notice the target Chad Bingham in one of the spas here) and into the little cavern with the big pool. Sometimes there is a guard standing at his post in front of the door, sometimes there isn't. If there is, drop a coin somewhere nearby to get him distracted.