A Druthonae is a kind of latent schism in the fabric of reality. Places where the boundaries of different realities, times, and places unexpectedly meet. Normally they are not 'active', that is the barriers between realities are intact and these kind of 'holes' in space-time are not visible, nor do they cause any ill effects. There is a natural resistance to one point bleeding into the other, it takes a large burst of energy directed at the weakest point in the barrier to open the schism and make it active. When the same points in space, time, and realities touch, it forms a bridge between the two points until the barriers close back up.
Destination
A single Druthonae connects two points, sometimes the connection flows just one way but most often the connection flows in both directions. Even if the flow of matter / energy can flow in both directions a Druthonae connects two points of space, time, and reality to each other and that is it. A Druthonae cannot be changed, moved, or altered by any known means to change the origin or destination.
Time Travel
The connection is relative and moves as time moves. So if a Druthonae allows passage to the past (or future) the difference in time remains constant. So walk from 1990 to 1925 then in 2025 you could walk from there into 1960 along a specific path of reality. Temporal Druthonae tend to be symmetrical, that is to say matter / energy can flow in both directions.
Reality
A Druthonae can connect any reality (i.e. subspace domain) and any universe (i.e. timeline) and always connects the same two. Passages far flung realities with a high Codivergance Factor (the factor of difference of physical laws / properties from one reality to another) tend to not be symmetrical (matter / energy can only flow one direction).
Origin
There is usually a kind of void between different points in time or reality that are not supposed to touch. These voids stop something from crossing from one moment to some place in the past or even from one reality to another reality. In some places this void is thinner and one reality or time can directly touch another moment in another reality or bridge two times in the same reality together. There is no known cause and it is believed that these are woven into the very fabric of reality and are thus naturally occurring. It is theorized that allowing matter and energy to pass between realities may be a naturally occurring way for a given reality to avoid eventual entropic failure.