Image of SCP-5557, captured by weather balloon.

Item №: SCP-5557
Anomaly Class: Euclid
Special Containment Procedures: The chamber containing SCP-5557 has been outfitted with HC-grade concrete walls, and is accessible only through a concealed entrance in a staff-only area of Salisbury Cathedral. The balloon within SCP-5557 has been covered with a blue, camouflaged fabric, and all flight paths coming in proximity have been redirected. Public reports of SCP-5557 are to be suppressed whenever they emerge.
Safe-class secondary anomalies produced by SCP-5557 are to be contained in as many standard containment lockers as is applicable for each item. Anomalies with higher classifications may be subject to alternative documentation and special containment procedures.
Description: SCP-5557 is an ovoid region of space ~25 metres in length, simultaneously located in a chamber below Salisbury Cathedral, England, and at an altitude of ~36,000 metres above the building. Viewing the space from any direction will give the appearance of a clear blue sky, regardless of objects behind it or external weather conditions. SCP-5557 is empty save for an immovable, indestructible hot-air balloon1.
Due to being simultaneously in two positions, possessing only one location, and therefore not being in either position, SCP-5557 represents a physical manifestation of a logical contradiction. Persons within SCP-5557 are capable of distorting baseline logical reality by extrapolating from this contradiction, in-line with the logical principle of explosion2. This extrapolation often occurs unintentionally or subconsciously, and prolonged exposure causes an exponentially increasing quantity of secondary anomalies caused by contradictory axioms.
Following 1966-06-12, incursion into SCP-5557 has possessed a 100% fatality rate among human subjects.
Testing: Formal testing of SCP-5557's properties began on 1966-06-11, after a series of incursions by civilians and preliminary containment staff (and the subsequent containment of resultant anomalies). A log of all tests attempted to-date is included below:

Date: 1966-06-11
Test Summary: D-0088 extended a long metal pole into SCP-5557, on the end of which was mounted camera equipment and a small releasable payload outfitted with GPS.

Test Outcome: Camera footage was normal until it passed the boundary of SCP-5557, at which point it began to display the views from within the chamber and from the high-altitude balloon simultaneously. Persons observing the compromised footage were able to extrapolate safely without triggering additional anomalies, suggesting a limit to the principle of explosion's effect in baseline reality. The payload was deployed, and fell simultaneously from both locations — it was recovered shortly thereafter, and is currently being stored in two separate containment lockers.

Date: 1966-06-12
Test Summary: Agent Garvey entered SCP-5557 via a gangplank laid from the floor of Salisbury Cathedral to the basket of the balloon. They were instructed to formulate the idea that they existed in two places at once, observe the results, and leave SCP-5557 without making any further deductions about the nature of reality.

Test Outcome: Agent Garvey entered SCP-5557, but did not proceed with the test, instead turning around as if startled. They then nodded slowly, placed the back of their hand to their forehead, and violently combusted.
A variety of scenes were then observed by monitoring personnel, including:

Flames engulfing the balloon
The sky within SCP-5557 rapidly switching from night to day, and to an unidentified third state
The balloon being replaced with a burned-out wreck of itself
A colossal metal pole outfitted with camera apparatus emerging from the distance
The sky being replaced with the interior of Salisbury Cathedral
Furniture on the balloon spontaneously rearranging
The sky being replaced with smoke, fire, and rubble (identified as the remains of Salisbury Cathedral)
O5-01 seated at the balloon's writing desk, surrounded by an unquantifiably immense pile of paperwork related to possible exploitations of SCP-5557
An unidentified man in business attire falling from the balloon, as if pushed

All scenes occurred simultaneously, and their significance (if any) is as yet unknown. Following the conclusion of this event, Agent Garvey has been seated at the desk with his head in his hands, unmoving.

Date: 1966-06-12
Test Summary: D-0088 was provided with a nonlethal electroshock weapon and was instructed to enter SCP-5557 and retrieve Agent Garvey.

Test Outcome: Immediately after entering SCP-5557, D-0088 was replaced with an instance of Agent Garvey's corpse (severely decomposed), which subsequently combusted. The sentence "Boys. Boys. This one's not worth the hassle, boys" was then heard in Garvey's voice from an unknown source.
Identical outcomes have occurred on all subsequent attempts by a human subject to enter SCP-5557, with slight variations in the content of the spoken message3 The actions of Agent Garvey have been designated an O3-Class Ontological Shift, and Garvey himself has been designated permanently MIA and formally censured.

No further testing of SCP-5557 is believed to be possible at the present time.

Footnotes
1. This balloon is equipped with a basket containing a small writing desk, chest of drawers, and a desk lamp plugged into a power socket on the basket's interior. All are immovable and therefore inoperable. Despite being suspended in mid-air, no burner or alternative propulsion method is present.
2. Formally, assuming contradictory axioms $P$ and $¬P$ yields an arbitrary theorem $Q$, as follows:

1
$P$
By assumption
A statement (e.g. All grass is green) is true.

2
$¬P$
By assumption
The converse of the statement (e.g. All grass is not green) is also true.

3
$P ∨ Q$
Disjunction introduction (1)
All grass is green OR another statement (e.g. the sky is red) must be true, since the first part is true.

4
$Q$
Disjunctive syllogism (2, 3)
Since all grass is not green, the sky must be red.

3. Most notably including "Poke it with a stick, what could go wrong" and "Boys shouldn't run with scissors".

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