A garage and using the warm up method JCL describes in other posts. I only idle for about 20 to 30 seconds then drive VERY slowly, never going over 2k rpm until I am out of the blue temp marking. This warms the engine a lot faster than simply idling for long periods of time.

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'03 Black BMW E53 3.0i 110,000+ miles
'03 Black Mercedes-Benz W211 125,000+ miles
'13 White Mercedes-Benz W2o4 New