If you feel like having your brain broken a little bit, here's a gameplay trailer for the forthcoming mod Portal Reloaded (opens in new tab). It adds a Triple Portal Device that, as well as the familiar blue and orange portals, also shoots a rectangular green portal that takes you 20 years into the future.
Test chambers in the future, distinguishable by their rundown appearance, can be changed by altering test chambers in the present. Objects from the future can also be brought back into the present, and the moment in the trailer where I saw a puzzle solved using two companion cubes that are actually the same cube but from different points in time is the point where my brain packed its briefcase, put on a little hat, and closed the door behind it.
Portal Reloaded is the work of modder Jannis Brinkmann, who has been plugging away at it since 2014. It will contain 25 puzzles and a "small and contained story, which is delivered through more than 100 custom voice lines." A Q&A section on Brinkmann's website (opens in new tab) covers the important information, like the fact that timeportals default to middle-mouse button, and keybindings can be changed. On the subject of cake, the Q&A declares, "This information is confidential."
Portal Reloaded has its own Steam page (opens in new tab), and is planned for release on April 19, 2021, which is exactly 10 years after the launch of Portal 2. As Brinkmann explains, "This mod is meant to be a celebration of all its achievements and an ambitious attempt to push its concepts even further."