The Enterprise crew encounters the Guardian of Forever in The City on the Edge of Forever--This episode involves the crew of the starship USS Enterprise discovering a portal through space and time, which leads to Dr. McCoy's accidentally altering history.
Portal part 1 - a friend of mine (I believe) is a medium. I've been trying to convince her to use her abilities for a long time. She developed a mysterious illness and was off work on disability. A few months later, suddenly a portal started to appear on her bathroom wall. We didn't put it there, we assumed her Angels did.