Paint the walls a neutral color as a base coat. Use paint in a matte or flat finish so any details you add later will be able to adhere to the wall. You can also paint the top section of the walls blue and the bottom section a neutral color.
Print some templates of plants and animals onto transparency sheets. The Resources section has links to a lion, monkey and a palm tree.
Project the template onto the wall where desired. If using a flashlight, place the light behind the transparency to project the image onto the wall. Move the light further away for a larger image and closer to the transparency for a smaller image.
Trace the image onto the wall in pencil.
Paint the images with acrylic craft paint and allow to dry completely.
Unroll green bulletin board paper and cut a piece that is a little longer than the hallway. Crumble the paper to wrinkle and twist the paper to create vines. Attach the vine to the wall with double sided tape.
Continue adding vines as desired.
Cut large leaf shapes from more green paper and add these randomly along the vines with more double sided tape.
Blow up small brown balloons to represent coconuts and add them to the palm trees with double sided tape.