Requirement: A hybrid bathtub-shower.
Steps:
1. Start to fill bathtub with water at the highest temperature until it's about 70% to maximum volume.
2. Then change the temperature to the coldest, and continue to fill the bath until perhaps 90% volume.
3. Then get in and bathe, until you feel uncomfortably hot (maybe this will take about 20m).
4. Then drain the bathtub. As the bathtub drains, you can apply soap and shampoo.
5. Take a cold shower (basically on the coldest temperature it allows).
The reason to do steps 1 and 2 is that your feet will be in the front of the bath, and will be the most vulnerable to heat, so you'll want the water there to be a bit cooler.