At "Yanov" you need to go to the ventilation complex - that's where the Oasis is located. To get into the tunnels leading to the Oasis, you must not go to the ground part of the complex, but go from the side of the railway embankment. The entrance to the underground part will look like a small building partially sunk into the slope. There are a lot of carcasses in the tunnels, and there are several zombified ones in the rooms.
Once inside, you need to walk to the boarded-up doorway, spread the boards, go through the doorway and immediately turn right. After that, you need to go straight to the closed door, on the right there is a pipe built into the concrete - you need to go through it to the next room. Coming out of the pipe, right in front of the exit, you can see another pipe, but with brackets embedded in it. You need to enter it and climb the brackets to the next room, directly opposite the exit is a similar pipe. You need to repeat the procedure and get to the next room. The pipe is closed by a lattice, so you need to turn left, where, after going through the corridor to the end, you can get to the room with columns.
This is a puzzle: if you go further, you will be teleported back. In order to solve the puzzle and get to Oasis you need to do the following: Walk through each row of columns in a straight line until you get teleported back. Now there should be four "white anomalies" between some of the columns, in order to get to Oasis you need to walk through them in order of how close are they to the room entrance, and the teleportation effect should be bypassed.

After solving the puzzle, you will arrive at the Oasis. The Heart of the Oasis can be found hanging on a tree. Once you pick it up two Psy-dogs will spawn in the room, you can either run away from them if you are unprepared, or use the water in the Oasis to your advantage( It regenarates your health, endurance and cures radiation) and kill them pretty easily.
You will receive a reward from the scientists if you hand over the artifact. Reward 7000 RUB's

*The location of "white anomalies" between the colums change after each emission
*After you solve the puzzle once, you can come back to the Oasis without having to solve it again