Say hello

Say Hello to Jim.
Gym stands lonely in a park.
You never see him being used,
Unless somebody is there after dark.
He is a help to keeping fit, 
Without monthly fees,
But lonely he stands every day, 
Beside the river and trees.

A tree, of which I speak about,
Is on the extra shot, 
It looks as if it's been there for years,
All gnarled and full of knots.