Here it is, in Poland (hat-tip to the Hermeneutic of Continuity).
The window can be opened from the outside. A person with a baby the parents are unable or unwilling to care for can pop the baby in and make themselves scarce. The baby will be scooped up by nuns on the other side and looked after. This is a modern version of a long-standing practice; in former times convents would sometimes have a wheel set horizontally into the wall like a dumb waiter: put the baby on the wheel, turn it so it goes inside, the baby is cared for and the parent or whoever remains anonymous.
Is it cooperation with evil? Of course: it is an extremely grave sin for a parent to abandon a child, even when the child's prospects are not too bad. The existence of these windows facilitates this abandonment, by ensuring that there will be no legal sanction against the abandoning parent. (Neglect and of course killing of children is illegal: normally abandonment would be at least neglect and probably killing.)
Furthermore, not only are these windows providing a specific mechanism for a person who wishes to commit this sin, but by making the sin easier and eliminating the legal risk they will certainly be making it more common, if only fractionally.
It is not wrong, however, to provide the window. The nuns' intention is conditional: that a person seriously considering abortion, infanticide or abandonment use the window instead, and perform a less serious sin with far less bad consequences for the baby. They do not intend that anyone abandon a child, any more than a person providing fire-extinguishers intends there to be a fire in which they might be used. Given that the provision of the window is a merely material, not formal (intended) cooperation with evil, it can be justified by reference to its consquences, including the possible scandal it might cause. Since the motivation of the nuns is clear enough, there is not likely to be scandal; nor does it seem likely that the existence of the windows will increase the number of times people abandon (or murder) their infants to the point where the scheme becomes the cause of greater harms than of good.
In this way it is a far clearer example of licit cooperation with evil than other putative examples, such as needle-exchange schemes for drug addicts, the provision of drugs themselves to adicts, or the distribution of condoms.