I love travelling overground on extended holidays: one trip travelling from one side of a continent to another, or around it in the case of Australia.
12000 miles in Greyhound buses round USA and Canada.
10000 miles by bus around Australia, including one 42 hour coach trip.
4000 miles by train around Europe
Many miles around SE Asia by train and bus
Many miles around South Africa and Zimbabwe by bus
Several hundred miles around the Galapagos island by boat
There are others!