You may choose not to untap Amber Prison during your untap step.
{4}, {T}: Tap target artifact, creature, or land. That permanent doesn't untap during its controller's untap step for as long as Amber Prison remains tapped.
NM-Mint - $1.00
Lightly Played - $0.90
Moderately Played - $0.80
Heavily Played - $0.70
Damaged - $0.50
NM-Mint Non English - $1.00
Lightly Played Non English - $0.90
Moderately Played Non English - $0.80
Heavily Played Non English - $0.70
Damaged Non English - $0.50