What's the orientation of the Rope Trick hole?

Question

The Rope Trick spell specifies

Holding one end of a 60-foot or shorter rope causes the other end to rise up until the rope is fully perpendicular to the ground. At the high end, a portal opens to an extradimensional space into which eight medium or smaller creatures can fit by climbing up the rope. The rope can also be dragged up into the space to hide the entrance and the portal itself is invisible.

Spells and attacks are unable to enter or exit the extradimensional space, but those within can see out of it as through a 3 by 5 foot window centered over the high end of the rope.

If everything inside the extradimensional space has not exited beforehand, it will fall out when the spell ends.

Our group has been playing under the assumption that the window is positioned vertically relative to the ground plane, because that's the way most windows we see are positioned. This would mean that you climb into the hole as if on top of a cliff edge at the end of the rope and you then have a view of the world as if you'd be looking out of any normal building window.

However, this seems to be in contradiction with popular depictions on the internet.

The difference would be surprisingly relevant to some standard strategies we have been employing.

How is the Rope Trick portal positioned relative to the ground plane/gravity/the rope?

Answer 1

It isn't defined

As you've noted, the spell description doesn't specify orientation. Windows are just openings and while most of think of a window on a wall, a window in a floor or ceiling is still a window and ropes can be pulled up into a vertical or horizontal window.

As user @MattVincent notes in a comment on the question, your spell description is not equivalent to the printed one. The changes are minor, but rope trick states (emphasis mine):

You touch a length of rope that is up to 60 feet long. One end of the rope then rises into the air until the whole rope hangs perpendicular to the ground. At the upper end of the rope, an invisible entrance opens to an extradimensional space that lasts until the spell ends.

The extradimensional space can be reached by climbing to the top of the rope. The space can hold as many as eight Medium or smaller creatures. The rope can be pulled into the space, making the rope disappear from view outside the space.

Attacks and spells can't cross through the entrance into or out of the extradimensional space, but those inside can see out of it as if through a 3-foot-by-5- foot window centered on the rope.

Anything inside the extradimensional space drops out when the spell ends.

It's up to the table/DM

If the orientation that you've been using has worked for the table, then you're good! If you want to keep it as such, you can. If you want to let your players pick an orientation at time of casting, you can.

And you can always change your mind if you think it's being exploited - but be sure to discuss it at the table so all understand how it works in the world you play in.

At my tables

We've imagined it in the same way that the image you link to does. A portal/window opens above parallel to the surface they're on with a rope dangling down.