When the level begins, you will be introduced to Kuzmich who will give a brief speech detailing the arms and equipment he has for sale. After which you’ll introduced to Shaman, the artifacts collector, who will brief you on what artifacts you’re going to be looking for during your trips to the surface and the Great Library. There is a panel next to his station that shows what items can be located and returned from the surface. When you bring him an artifact, it will be crossed off the list so you can easily see what you still have left to look for on subsequent trips. You can only carry 5 artifacts at a time before your bag is full and you must return to the base and trade them.
Returned artifacts will be evaluated by Shaman, who will give you an amount of Military Grade Rounds (MGR) based on the value of each item. You can then use the MGR to purchase weapons and equipment from Kuzmich. Keep in mind that you will be using a lot of filters and that each time you buy one the price will increase, so try not to purchase too many up front. The weapons you choose to purchase are entirely up to you, but you should be saving up to purchase the Environment suit as it will extend the life of your filters and keep you from taking damage from extreme weather you will encounter on the surface.
As you open the doors that lead into the first sewer area, you will be told that you also have the task of replacing light bulbs in the empty sockets you’ll find scattered around the map. Again, you only have so many before they run out, but you can replenish your supply from the light bulb box near the sewer entrance. This is not a mandatory task, but it does help improve navigation of the level.
The map seems rather small to begin with, but you will find that there are doors and gates to unlock that allow further progress into the level – and shortcuts back to base. In general, if you are searching for artifacts thoroughly, when your bag fills up use that as an indicator to start looking around for a shortcut to open that will lead you back to base. You can then use this shortcut to get back to where you were scavenging and continue on. Be sure to use the Save Door when you come back to base to save your progress as well.
Enemies on the level are randomly spawning Nosalises with Lurkers and Librarians in set positions, most of which can be avoided completely. Also, Librarians can still be stared down just as in Metro 2033. One of the biggest obstacles to be aware of is the fact that many times when you return to base, Nosalises will attack in packs as you wait for the doors to open. Bear this in mind when returning to base.
The player can explore the level as long as they want, up until the Secret Subway Map is obtained. As soon as that artifact is returned to Shaman, the level will end regardless of how many other artifacts have been retrieved.