Mö x I: the circle of black points marks an absolute
deformation retract of this space, and any regular neighbourhood of it has again boundary as a Klein bottle, so Mö x I is an onion of Klein bottles
Alternatively, one can visualize the solid Klein bottle as the
trivial product, of the
möbius strip and an interval . In this model one can see that
the core central curve at 1/2 has a regular neighborhood which is again a trivial
cartesian product: and whose boundary is a Klein bottle.