As a gateway:
* The ancient archway served as a portal to another dimension.
* The website is a portal to all the information you need about the city.
* The internet is a portal to a world of knowledge and entertainment.
As a website:
* I used a travel portal to book my flight and hotel.
* The company uses a student portal to manage their academic records.
Figuratively:
* Her smile was a portal to her inner joy.
* Music can be a portal to different emotions and experiences.
In a specific context:
* The game developer created a hidden portal in the game world, leading to a secret level.
* The astronauts used a space portal to travel between planets.
Remember to choose the meaning of "portal" that best fits the context of your sentence.