If you are toying with the idea of running a campaign involving time travel but are seeking inspiration for that killer idea to set it all off - read the list herein!
Encapsulated in a sentence or two, this product contains an hundred core concepts each capable of spawning a whole campaign. They are divided into different eras, and for each provide suggestions for games in which the characters - your players - can either be the time travellers or be native to a time and place that is visited by time travellers. Many will lead to truly epic campaigns, that could keep you and your group entertained for months or even years of gaming. Some involve known historical personalities or events, others are more general. Some involve aliens and some it's human beings but from the past or the future...
This is only the start, of course. Once you have picked out a concept that suits, you'll need to choose a game system and work out all the specifics, and then devise the actual adventures that your group will play.
Whilst the examples here are firmly rooted in the history of Earth, many of them could easily be retooled to occur on your favourite fantasy world instead. These kind of adventure ideas are exceptionally good for 'crossover' events - I once ran a game in which 1990s Americans from Florida found themselves in the world of Conan the Barbarian and great fun was had by all. It can be (as in my game) particularly spectacular when dropped into a campaign unexpectedly - they'd been playing a police procedural set in Florida!
Read through this, muse on the possibilities, and enjoy...