Cannot for the life of me remember the name of this one....

[Where is this book?]

I am looking for the title and author of a sci-fi book that I read a long time ago. The plot is that people are doing some work on the bottom of the ocean and they find an entrance to an underground society that is far more advanced than our own. No one works, sex is for recreation, and when people get old, they have their minds transferred into the body of a newborn. Travel is done in pods that have doors that close without showing any seams. Towards the end of the book, the visitors are told they can never leave because the underground people dont want their existence known to the world at large. Two of the visitors try to escape to Boston, but the underground people catch them in the act and allow them to go to Boston, but 200 years in the past.
HELP ME FIND THE TITLE TO THIS BOOK. PLEASE!!!

 

[Matteo]

Sounds a lot like Abduction by Robin Cook: Abduction (novel) - Wikipedia, the free encyclopedia but that was fairly recent (2000).

 

[Where is this book?]

That's it!!!!! Thank you very much Matteo

 

[Matteo]

Glad to help.