Building "cold room" in our garage or fix the cold room

I'm at an impasse, I have a home with a "cold room" of sorts, but it's "broken" for all intensive purposes. I need cold storage for root veg asap!

Said room is a concrete room with only one exterior wall. It is located indoors under our front hall. no venting, and smells awful!
The exterior wall is where my front door is and would be extremely difficult and potentially costly to vent there.
Do I have indoor venting options?

I also have an insulated but unheated attached garage.
Could I simply build a small cupboard or room on the attached wall?

Weather here goes from -45C (-49F) in winter to +40C(104) in summer.

Coolbots are not CHEAP, but they are inexpensive solutions. http://www.storeitcold.com/ You could convert any room with it. I think I will be getting one of these at some point. They have really good resources on the plans page including cost estimates. Use their tips for any cold room regardless of whether you use their product or another one.

I wish they had a freezer version...