There is nothing wrong with COC. It works fine if you are playing on a PC, and I use COC to view and make notes on my cells when working on them. But a player may find it inconvenient or impossible to use the COC command to get into a interior cell from the other side of the world map.
So there are two alternatives.
One, a map marker and a back door into the cell you want to get to quickly. This works quite well and I have created such an implementation.
Two, a way to enter the cell without the intervening stop, as in fast travel directly into the cell. Since fast travel into an interior cell isn't possible with this engine, a spell seems a reasonable alternative. A spell is the approach I stated I was investigating in my previous post.
I hope this addresses your questions.