a Buddhist statue that has been hidden from public viewing
「秘仏」は英語で次のように言えます。
ーa Buddhist statue that has been hidden from public viewing
「一般公開されていない仏像」=「秘仏」
例:
My family and I were able to see a Buddhist statue that had been hidden from public viewing for over 20 years.
「私の家族と私は、20年以上の秘仏を見ることができた」
ご参考まで!