The white housefly that ended up in a Klein bottle*
housefly is made of porcelain and nichrome wire (2020)
The Klein bottle* is a one-sided non-orientable topological space** without inside and outside - inside surface smoothly connects to its outside surface without an edge.
Therefore, the housefly will crawl around forever without ever encountering a boundary or falling over an edge. A true Klein bottle, that does not self-intersect, is not constructible in our 3D system of objects and needs "time" (t) as a fourth dimension, i.e. it could be constructed in xyzt-space.
**Topology is a branch of mathematics, concerned with the properties of a geometric objects that are preserved under continuous deformations, such as stretching, twisting, crumpling and bending, but not tearing or gluing.