I had a hard time choosing one, because I'm a greedy person LOL!!! Then I figured it out! My answer would be The Holodeck in the Star Trek series. Going into the Holodeck means I'll be able to go to any fictional place that I want HA HA HA HA HA HA...So depending on my mood, I can play as Sherlock Holmes or become even an elf in The Lord of the Rings or whatever I want in the course of that one day instead of just being in one fictional place LOL!!!
In the wikipedia page, it's said that the Holodeck is good for entertainment purposes but it can also be used for training purposes. How cool is that? Ever since the first time I saw it years and years back on TV, I've always been daydreaming about being able to use it.
Here's more info and photos on Holodeck (I grew up with Star Trek: The Next Generation with Captain Picard as the leader). Just looking at the photos brought me back to the past he he he...
What would your answer be like, readers?