Item #: SCP-XXXX

Object Class: Safe

Special Containment Procedures: SCP-XXXX is currently contained in Dimensional Unit 74, former Site 26. The area around the site should be guarded by at least five level 2 security officers, protecting SCP-XXXX, the main and secondary gates to the yard. Standard work shift - 24 hours, starting from 4AM local time (EEST). After a shift, security personnel are to move to living quarters in nearby Site 54. Security cameras are placed on the outside and inside of the apartment. Access to SCP-XXXX requires a level 2 clearance. All keys that open SCP-XXXX's lock recovered from Foundation personnel working in former Site 26 are to be stored in Site 54, Object Storage 7.

A Class-B amnestic is to be administered to any non-Foundation personnel detected attempting to enter Unit 74. The doors in the stairway behind SCP-XXXX must be left open upon entering the following rooms. All recorded tests and expeditions from SCP-XXXX are to be logged and sent to Site 54 for analysis and archiving. All expeditions must follow the rule set XXXX-Path-b.

Description: SCP-XXXX is a metal door painted green, located in the entrance of an abandoned Soviet-era apartment, in ████████, Lithuania. It measures 1.9 x 1.5m. There is a vertically-oriented window placed in the center of SCP-XXXX. Adjacent to it, an extension made out of the same material as SCP-XXXX. This extension has an electronic door buzzer, containing 4 buttons, with blank writing spaces next to them. These have not been functional since the establishment of Site-26. It also contains the lock for SCP-XXXX, which has visible rust around it. Though the extension can be unlocked from the inside, the anomalous effects of SCP-XXXX will not occur upon opening the door. A staircase made of crackled, broken concrete leads to SCP-XXXX, alongside which, 2 short concrete walls extend to the top. On them, metal railings painted green are attached. A stairway with stairs leading up and down is present behind SCP-XXXX.

The anomalous properties of SCP-XXXX are only present upon unlocking and entering the apartments beyond it. These effects started to manifest after a loud explosion was heard outside of the apartment during event S26-X in 1█-09-20██. No physical damage to the building's interior or exterior has been made. All Foundation personnel present inside the building and in a ~5m radius outside spontaneously disintegrated, leaving no trace behind.

During expeditions, it was noted that every staircase in the stairway contains a different amount of steps. The length of the staircases and the height of the stairwell do not correspond to the outside dimensions of the apartment. Each staircase ends with a platform leading to another staircase. The walls adjacent to the platforms contain windows with wooden frames. The stairwell seems to indefinitely extend vertically, with the furthest traveled distance of approximately 17km upwards.

The doors on every second platform are identical to each other. The doors are numbered from 403, ending with an unknown number due to the spatial effects caused by the staircase. The flats behind every door are identical to each other (see List SCP-XXXX-R for list of rooms). All object in these rooms are completely static and no damage inflicted is apparent. These rooms are furnished with exactly the same furniture. Every room seems missing a source of electricity and the cables are soldered in to the walls. Wooden stairs in these flats lead to a single 3 x 3 x 3m room. It contains an exact copy of SCP-XXXX, placed in the room's southern wall.

Subjects unlocking and walking through the copy of SCP-XXXX are returned to the beginning of the stairwell behind SCP-XXXX and the door automatically closes behind. If opened again, subjects are returned to the outside.

Entering the apartments in any other ways, e.g. through the windows, results in no anomalous effect occurring in the stairways. Four floors have been counted, the rooms are unfurnished and seem to have been abandoned during construction. The doors are missing and only the doorways are left. The would-be basement area is sealed off by a wall. The copy of SCP-XXXX is missing from the second floor.

Interior of the building (affected by SCP-XXXX or otherwise) does not match visual records of Site 26.

Addendum XXXX-A: SCP-XXXX-A is an oak wood door, located in the basement of the stairway behind SCP-XXXX. The lock has a key inserted and fused to it. No attempts to remove this key have succeeded.

Behind SCP-XXXX-A, a room, measuring 6x6x3m is located. The ground is covered by rust, so is the bottom portion of the walls. The west wall contains a painted oak door, which leads to another room (10x10x4m), with a metal table and a chair1, which are fused to the floor. The table has a sheet of white paper placed on it. The paper has writing on both sides which changes with every expedition, ending with the final word (END) on 20██-11-██. The writings have been documented and if ordered, an interrogation log can be read (See Document XXXX-DL). It is assumed that the document explains the cause of the event S26-X (see above). The search for the subject, the mentioned object and the bodies of personnel is ongoing.