Again, thanks in advance if you can provide any help...

There were a series of books that were based in Victorian times (including a sketch book and travel notes as if this it were a Victorian expedition). The beginnings of the story in the first book were similar to HG Wells stories - there was a way to get into the center of the Earth, but then things diverged - castles, magic, demon-like creatures, oceans, etc.

The series was pretty interesting and I thought I'd like to read it again, but I simply can't remember the name, author, or anything and I haven't been able to find it through traditional searching. I believe that the series was written not long before I was reading it (in the late 80s).

Any help would be greatly appreciated and thank you regardless!