Drop down and search the right side to find [5 SKILL PILLS] on the counter. There's a safe in the behind the concierge counter, but you require a combination first. On the left side of the area you'll find [(3/4) ALCOHOL] on the counter. Inspect the coffee machine for a short optional line from Joel. The ladder can be found against the nearby scaffolding.
Before placing it against the wall in the corner (to reach the stairs), place it against the side of the nearby scaffolding to find [10 PARTS] on top. After climbing the ladder to reach the stairs, first head past the destroyed stairs to your right by walking close to the wall; this leads to a suitcase in the corner on the other side of the area with a [NOTE TO STAFF] that includes the combination of the safe found below. The safe contains [(1/2) EXPLOSIVE], [4 REVOLVER AMMO], [50 PARTS] and the [SHIV: REINFORCEMENT TRAINING MANUAL].
Finally head upstairs and go outside. Sneak past across the roof and enter the window on the other side; immediately push forward and go around the corner to strangle the marauder while he's still behind the desk; he should drop a Lead Pipe - possibly useful for later. Move down the hall when the coast is clear and strangle the marauder in one of the rooms to the right when he's not looking. The cabinet with the TV on top contains [(3/4) BINDING] and [(1/2) BLADES].
There's a [HEALTH BAR] in the destroyed vending machine in the main hall. Head down the other hall to the (initial) left and strangle another marauder inside one of the rooms - this shouldn't be too hard and yes, the guy playing at E3 sucked at this game (yeah, it was just for 'show', but he sucked nonetheless). One other marauder is searching the other set of rooms, so dispatch him too before searching the place.
The set of rooms on the left side of this hall (with the open window) contain [(1/4) BLADES] and some [(1/2) ALCOHOL]. The other room(s) contain a [HEALTH BAR] and grant access to a balcony with a [BASEBALL BAT], [EXPLOSIVE] and a [HEALTH BAR]. Head back to the main hall and go around the corner, then head upstairs. Wait for one of the marauders to come close, then dispatch him and move down the hall.
There's another marauder searching the rooms to your left (even though there's not much to be found, other than a [HEALTH CAN]). Proceed through the hall and strangle another marauder in one of the rooms across the large hall. Search them for [(3/4) RAG], [(1/2) SUGAR], [7 PARTS] and [5 SKILL PILLS]. Head outside and hop through the window, then hide behind the bed until the nearby marauder passes by, then strangle him. Search the rooms for [(1/4) BLADES] and a [HEALTH CAN], then proceed through the hall. At the intersection you can optionally head back to the main hall and move to the far end to explore more rooms (and kill more marauders). Inside these rooms you can find [(1/4) BLADES], [5 SKILL PILLS], [(1/4) RAG], and you can start an optional conversation with Ellie in the bathroom. You can find [10 PARTS] in the room with the hole in the floor.
Head back to the main hall and move towards the burning barrel, then turn left and head upstairs to reach a room with an open elevator. The suitcase in this room contains [ALCOHOL] and [(1/2) EXPLOSIVE]. Open the elevator doors, then move down on the elevator and boost Ellie up to trigger a scene.
Dive down to find [10 PARTS], then proceed through the doorway. The right path leads to a storage room with [(1/4) BLADES] and the doors to your left lead to nowhere, so you have no other choice but to move straight onward through the doorway with the exit sign next to it. Wade into the water and dive, then move through the doorway, swim through this room with bodies and emerge in a larger room on the other side.
The smaller doorway leads to a storage room with [25 PARTS] and a [SHIV], the larger doorway (with the 'West Tower B1' sign) leads to a closed gate. Head back to the large area and position Joel so he's facing the large doorway, then dive and swim through the tunnel to move beyond the gate. Proceed through the next tunnel and head inside the first room to your left to find a [HEALTH CAN], [(3/4) EXPLOSIVE], [(3/4) RAG] and [(1/4) ALCOHOL]. The room on the right side of the hall contains [(1/2) BINDING] and [3 RIFLE AMMO].
Unfortunately, as soon as you activate the generator in the adjacent room, several Stalkers and a Bloater will close in on your position, so you might first want to head up (via the destroyed concrete floor) and search the desk in this room to find [5 PARTS]. The restroom contains a [WOODEN STICK]. The room across the hall contains the [HOTEL KEYCARD], though you'll be assaulted by several Stalkers once you grab it. These terrible creatures will actively hunt you; sneaking past is not an option, so you'll have to kill them as soon as you spot them.
Proceed through the other hall, adjacent to the destroyed floor, and search the laundry room to find [10 SKILL PILLS]. The doorway to the left leads to some stairs that bring you back from where you came from; the big doorway at the end of the hall, however, with the exit sign above it, leads to a hallway with spores; at the end of this hallway is a (locked) door that is your exit. What you'll need to do is activate the generator in the room on the lower level and make your way to this door (provided you have the Hotel Keycard). Unfortunately, a Bloater will pretty much block this hallway, so you'll want to 'lure' it to the laundry room, then rush to the exit. First use the keycard reader, then head through the door; once you do that you're safe. Alternatively you could try taking out your enemies, but that would drain your resources more heavily. You'll probably only need one Health Kit after making your escape to patch yourself up.
Head upstairs and search the restroom for [2 REVOLVER AMMO]. The adjacent room contains [5 SKILL PILLS] and [5 PARTS] (the parts are in the desks' drawer), plus a Workbench, so take your time to upgrade some of your weapons. The room on the opposite side of the hall (the door of which is initially closed) contains [10 PARTS] and a [(1/2) BLADES], should you need some additional parts for upgrading.
When you're all done, head through the door at the end of the hall and sneak behind the fridge as two marauders enter the area. The first one will soon enough investigate the nearby storage room, which is an excellent moment to strangle him. Inside you'll find [5 PARTS], [SUGAR] and [(1/2) EXPLOSIVE]. The second marauder will soon inspect the main kitchen, so sneak behind him (don't trip over anything that could make a sound) to dispatch him quietly. You can find a [HEALTH BAR] in the corner next to the microwave.
Two more marauders are searching the lounge area. Wait for the one closest to you to inspect the right side of the room and strangle him when he's turned his back on you. The other can now be taken out rather easily by approaching him from the back as well. Search the benches in the far right corner for [5 PARTS], then place the ladder in the opposite corner against the wall to continue. As you climb up, a scene will play; be sure to tap square at the appropriate times.
After the scene, move through the rooms and turn left, then move close to the wall in order to reach the area beyond the destroyed floor to find [13 PARTS], [ACRETION (COMIC)], [(1/2) RAG] and [(1/4) BLADES]. Head back to the hall and go downstairs. Inspect the second room to your left - the women's restroom – to find a [FIREFLY PENDANT (COLBY REED)]. Further down the hall you can find the [MELEE: KNOTS (TRAINING MANUAL)], which increases the amount of times a melee upgrade can be used by 1. Search one of the drawers near the intersection to find [(1/4) EXPLOSIVE].
Pittsburgh After Restaurant (plus Comic and Firefly Pendant)
Continue by hopping over the table down the hall. Enter the stage/diner room and check the corner with the light screen to find [4 PARTS] and [(3/4) ALCOHOL], then move over to the piano. Joel can 'play' the piano, but its real use is to reach the balcony on the other end of the stage, so push it in that direction and climb up. Move all the way around the balcony to find [5 PARTS] and [(3/4) BINDING] at the other end. Move through the last room and go outside to trigger a scene.