boggle the mind

to boggle the mind (stop the rational thinking process by virtue of being too fantastic or incredible; have difficulty imagining or understanding something)
It boggles the/my mind (to do sth/that)

Example 1: The/my mind boggles at the amount of money they spend on clothes. — Уму непостижимо, просто голова идёт кругом, сколько денег они тратят на одежду.

Example 2: It boggles the mind to think about how much money was wasted.(CDAmE)

Example 3: He boggled at the suggestion.(=be very surprised and uncertain about how to deal with it) (CALD)

Example 4: It boggles the mind that John should have been inside a flying saucer!(САм)

Example 4: There are conspiracy theories proposed and defended by college educated people. Some of these conspiracy theories are so outlandish and ridiculous that it boggles my mind to read about them. (www)

see also
[coming or going]
[сносить крышу]
[уму непостижимо]
[голова идёт кругом]
[ум за разум заходит]

Examples from NTC's
boggle sb’s mind — to confuse sb; to overwhelm sb; to blow sb’s mind.

The size of the house boggles my mind.
She said that his arrogance boggled her mind.