Where would you least expect to find a troll? Near water! Perfect hiding
place to lurk and stalk. Though trolls usually prefer to use the banks
of the river under the bridge, and the reason player's cannot climb on to them
is that they are invisible and only trolls can see them if they cast a magic
spell that is only available to the secret society of trollhood which you
cannot join because it's secret.

There you have it.

~/A