[Suze65]

Forget blue Peter ! I've looked at your other post and I think you have a North African Graeca, usually these only have a short hibernation compared with European Graeca. About 8 weeks. Has he/she been left to wind down naturally, this is ok or alternatively you can do a controlled wind down. As for a box of straw in the shed or garage, now the time improve on that a little, a wooden box, that has been fully insulated , with electrics , so you can plug in a small tube heater, which is plugged into a thermostat, set at 6c . So the temps don't drop below 6c in the coldest weather.
Alternatively you could go for a fridge hibernation, I will let someone else explain this, as I've never done it.
Rather than straw, you can use shredded paper ( the small type) or even top soil, which he will dig down into. Straw and hay can have spores in it, which can cause respiratory problems.
Having said all that, most importantly, is that your tort is a good weight before starting to wind down, and is in good health, and has not had any recent health problems.