Fiction in which the entrance to another world / another time / another place is via a thing.

Things you can hold in your hands or wear, such as (but not limited to!): jewelry/jewellery, pocketwatches, glasses, cups, trophies, magic stones (smallish) and gems, statues, figurines, music boxes, desk-top globes, paperweights, snowglobes, clothing, books, etc.

Ingestibles count (food, potions, anything eaten or drunken).

When a port key is required in conjunction with a gateway (i.e. magic glasses + a painting), please add the book to both relevant lists (i.e. Objects and Mirrors & Paintings).

Is your Port Key...
- an item of jewellery or other bling? Please consider ALSO adding it to the list here: https://www.goodreads.com/list/show/1...
- a loose magic stone or gem? Then please consider ALSO adding it here: https://www.goodreads.com/list/show/1... (Standing stones and stone circles don't belong here anyway - see Portal is a Ruin below!).
- a book, there is a pretty neat "Book-Jumping, Book-Travelling" list in existence already here: https://www.goodreads.com/list/show/1... (it's okay to have overlap - better listed twice than not at all!)
- glasses? Here's a list for Magic Glasses as well: https://www.goodreads.com/list/show/1... (again, better to have it on both lists!)

Here are magic portals to other portal lists:
Portal is in or on Water https://www.goodreads.com/list/show/1...
Portal is in Forest https://www.goodreads.com/list/show/1...
Portal is in Ancient Ruins (Castles, Stone Circles, etc.) https://www.goodreads.com/list/show/1...
Portal is in a House or Existing Building (i.e. Wardrobe, Attics) https://www.goodreads.com/list/show/1...
Portal is a Painting or a Mirror https://www.goodreads.com/list/show/1...
Portal is through Fog or Mist https://www.goodreads.com/list/show/1...
Portal is in Lab or by Experiment https://www.goodreads.com/list/show/1...
Portal is Transportation related https://www.goodreads.com/list/show/1...