The Lost City

One the most dated of the books.
The science in this book is irrelevant today.
In the early 1960s there were a couple of satellites put up to bounce radio signals around.
https://en.wikipedia.org/wiki/Project_Echo

The bigger problem is the portrayal of the Indians and the Mongols.
It's a pretty exciting story but very much of its time.
Modern readers would find it ridiculous that they would have to spend almost
two months just to get to their target site.