Similar movie...help with title, please!

Hi,

I am trying to get the name of another "Hollow Earth" themed movie that I saw in the 80's...it could have been a TV movie or made for the big screen. In any case, I saw it on television.

It's set in the late 19th or early 20th century. There is some link to Iceland or Scandinavia I seem to remember, and a curious brass instrument that leads them to the entrance (and exit) of the world beneath. It's found at the beginning of the story in a junk shop? not sure about that but, anyway, it is key to the plot and the adventure that follows. They bring it back at the end I seem to remember, too.

When they are down there having their adventures, a couple of the party go off down a separate passage and they look down into a cave where there see lots of people in funny windowed buildings. The folks inside are obviously much more advanced technologically and are living and working down there completely self-sufficient. I think they decide not to tell anyone else what they have seen.

That's all I seem to remember...

If anyone can help, please do!

Thanks.

Sean.