Mysterious Abandoned Building is a Windows adult game by Zell23, made with the Others engine and presented through 2D animated art. You play a male protagonist trapped in a decaying multi-floor building filled with dim hallways, odd rooms, and aggressive creatures. Gameplay centers on careful exploration, environmental tension, and survival-style movement between floors, with scripted encounters and enemies. The tone is claustrophobic horror rather than straightforward combat, and players must watch for clues, avoid residents, and endure frightening confrontations.
The current release is Demo v1.27, dated April 29, 2024, and development is ongoing. It is English, uncensored, and runs on Windows. The latest changelog adds two adult animated sequences to the test map, Mizuhime and Squeezing Nest, while adjusting the avoidance input to X then D and changing the debug key from D to W. It also revises monster dot-map graphics. Mizuhime is a waterhole creature that attacks careless players, and the nest monsters capture prey, with some victims beyond rescue.
Developer's description
The game takes place inside a decaying, multi-floor abandoned building filled with dark corridors, strange rooms, and hostile creatures. The focus is on slow exploration, environmental tension, and navigating the building’s floors while encountering enemies and scripted events. Each update typically introduces new rooms, enemy animations, or mechanics, and reflects the author's iterative development style. Unlike his more combat-focused projects, Nazo no Haibiru leans into a claustrophobic horror tone, highlighting tight spaces, surprise encounters, and survival-style progression. Players must explore carefully, pay attention to environmental clues, and avoid or endure encounters with the building’s residents.
Demo v1.27
[add]
・Added two H anime to the test map (Mizuhime, Squeezing Nest)
[amendment]
・Changed the avoidance motion to X→D key (and changed D's debug key to W)
・Some modifications to the monster dot map graphics
★Character introduction
[Mizuhime]
A monster that appears in the waterhole. It clings to your feet to squeeze out the milk that approaches you carelessly.
[Sperm-milling nest]
Monsters with powerful powers may be building webs and capturing prey. The way prey is managed differs depending on each monster, but the captive victim is no longer sane and cannot be saved.
Sometimes you need to hide in the forest in order to evade surveillance.
Demo v1.26
[add]
・Added two H animations to the test map(
Red Hood Venomhayes
)
[amendment]
・Some modifications to the monster dot map graphics
・Make the gallery easy to understand (may be heavy)
Since adjustments are being made around the HP system, strange behavior may occur
★Character introduction
[ Red food ]
A monster wearing crimson clothes all over its body. They don't speak the same language and will attack you if they find a human.
It's like I'm collecting something while wandering around in the ruins...
[ Venom haze ]
A monster that spews gas 〇〇 from its body. His face is covered with a gas mask, so it is impossible to see his expression. As you approach defenselessness, you will be in a 〇〇 state in no time...
Demo v1.25
[add]
・Added two H animations to the test map(
Mimic Ghoul
)
[amendment]
・Some modifications to the monster dot map graphics
★Character introduction
[ Mimic ]
A monster lurking inside a box.
When the protagonist approaches, he reaches out and tries to catch him.
[ Ghoul ]
It wanders around in ruins like a zombie.
Demo v1.2
[add]
H animation on the test map
Two added
(
Imp · Monitor head
)
[amendment]
-Organize menu screens
・Some modifications to the monster dot map graphics
★Character introduction
[imp]
Lower devil. He appears as a servant of a high-ranking demon and attacks the protagonist.
Basically, the semen is expressed by the tail.
[monitor head]
A creepy monster with a mechanical head.
When it finds the main character, it not only chases after it, but also seems to have various abilities. .. ..? ( Demo not implemented
Vaginal live commentary
★Organize menu items
The menu has been renovated, and the equipment section has been divided into basic equipment and selective equipment.
Items that affect the main character's condition are summarized in selected equipment, and the tools section is necessary for solving puzzles
I'll just do it. Selective equipment can be attached and detached.
Player reviews
Player rating5.0 / 5 · 3 ratings
Written reviews3 · avg 4.7★
Positive (4–5★)100%
Latest review2025-11-30
What players say
Most reviewers liked it, praising animations and variety despite its gallery-like structure.
5★2
4★1
3★0
2★0
1★0
Players like
Good animations
Variety of monster girls
Common complaints
Limited structure and exploration
Best for players who enjoy monster girl galleries and good animations.
Summarised from 3 written player reviews.
Salvos2025-11-30★★★★★
There's a fair bit of content here, though they aren't structure. Most of them are like a gallery view, but what is here is good. File download from VikingFile will be flagged as virus, I believe this has more to…
Tobi255e2025-11-29★★★★★
Its basically just a gallery but animations are good and theres alot of variety lots of diffrent monster girls and mechanics that im sure will be expanded upon, such as the clone feature which lets monster girls attack the clone…
KangaroohKick902025-11-28★★★★★
This reminds me of 3 of my favorite games of this genre A LOT. The animations are very very good. , the Girls on the other hand have a lot of variety. and I like most of the ideas that…