Phrases Expressing Curiosity or Wonder

My mind is boggled.

C2

Meaning

I am completely baffled or astonished.

Example sentences

John: 'The complexity of the system completely boggles my mind.'<br>

Alice: 'I know; it's overwhelming.'

John: 'It is a monumental undertaking.'

Alice: 'The sheer scale of the project boggles my mind.'<br>