As the title says, plain and simple. Name one thing you wish to do before you die. It could be anything that has a chance of being achieved within your lifespan. Anything you want, it could be climbing the Everest or having a five-some or discovering a cure for cancer.
If your life is cake, then this one thing is the icing, so what is your one wish.
I wish to go into space before I die. I just want to experience the unending vastness and see Earth as a blue marble. I have always been fascinated by space and i would consider my life complete if I could do this.
Rule: Whatever you wish has to be reasonably achievable within your lifetime