Our Last Adventure (2016)

Going back to the place of adventures where their imagination roamed free, two best friends rediscover their childhood tree house. Phil attempts to convince his best friend Steve to relive their favorite childhood book. With Steve not being able to cope with Phil's inevitable and cancerous demise, Steve accepts Phil's request and escapes to the fictional world. Travelling in their imaginary submarine they battle an ancient, sea creature where Phil helps Steve accept the reality he has been avoiding.