I've rationalized a way to combine period-themed PM (pirates, knights, western, egyptian, etc...) with modern theme: you can pretend you are a present-day adventurer mounting an expedition to discover, unbury, and explore ancient or antique treasures, civilizations, and cultures! Or you can expand it into sci-fi where a modern expedition on a ship (like the titan with a fleet of expedition boats) gets sucked into a time vortex and ends up traveling into the past.... the possibilities are endless! A titan can even be retro-fitted to become an exploration ship command center if you really wanted.