Where in the World is Liberia?
The main way to get to Liberia is to fly
into Monrovia. Flights don't come or leave every day of the
week. It's not a major tourist destination (my kind of place!) so
you need to be flexible. And, if you are really flexible, get out
of the capital and explore up country in the interior.
The border along the southeast is along the Cavalla River. Near Zwedru, during my Peace Corps days, we would swim across the river to the Ivory Coast. One village chief whom I met near Fish Town said that if I ever manage to come back, he'd take me for a canoe ride on the river. You can do that as far south as Harper.
It's also possible to cross into Sierra Leone near Voinjama and into Guinea by way of Ganta.