Pre-order
Of course, there are rules.....
Rule number one:
Travel can only occur at destination points during the previous lifetime of the traveler.
These destination points are random.
Rule number two:
The traveler only has enough energy to maintain contact with the arrival world for approximately ninety seconds.
Rule number three:
The traveler has no ability to interact with the world they have traveled to ......
... the traveler can only observe.