Despite not being seen very frequently, the Astral Prism is one of the most important story locations in Baldur’s Gate 3. No matter what you decide in your own run, you need to make your way into it.
Baldur’s Gate 3 Act 1: How to enter the Astral Prism
Baldur’s Gate 3 lets you enter the Astral Prism three times, once once in each act. As part of the main plot, you’ll enter the Astral Prism twice. However, you can skip your chance to enter the Astral Prism late in Act 1.