On one wall, I would paint a picture of a tropical rainforest. There'll be greenery everywhere, colourful flowers blossoming, a stream flowing through, and possibly some birds and animals.
On another, I would paint the Great Barrier Reef, with colouful sea creatures and coral reefs. Maybe even myself scuba diving!
I don't know what to do with the other 2 walls...
But if I have to paint all the walls, I'd do this!
One wall will be winter, with snow and a snowman.
One wall will be spring, with a field of flowers under a small hill
One wall will be summer, with the beach and the sunshine and surfers!
One wall will be autumn, with red and gold leaves falling from the trees!