Is Wave Echo Cave connected to the Underdark?

Question

Inspired by RedTera's comment on DaleM's answer to another question:

I also thought Wave Echo Cave was connected to the Underdark but couldn't find where it was mentioned. Do you have reference?

Given that I'm currently running this adventure and do plan on extending the adventure beyond the end of what's written by going into the Underdark, I would be very interested to know if this is indeed the case. I looked through the pages that describe the Wave Echo Cave dungeon and couldn't find anything myself...

(Note that I could easily make up an entrance to the Underdark if it turns out there isn't one, but if there is, might as well use what's there.)

Answer 1

No, it's not connected?

There's no mention of the Underdark in the Lost Mine of Phandelver adventure. The only references to the Underdark and Wave Echo Cave on the internet are references to people adding it.

So there does not seem to be a published connection.

However... how do you prove a negative? Certainly there's nothing published that says that there isn't a connection. And on the map in the adventure both the dark pool and the booming cavern have boundaries not shown on the map.

For reference, this map of the Underdark shows that it's not that far from Wave Echo Cave to parts of the Underdark.

So... no, not according to any published information. But there reasonably could be. There's nothing that contradicts a published adventure in the future connecting them.