Last night, I also talked with Mrs. Barrett, who taught fourth grade when I was in fourth grade.
My teacher that year was Mr. Armitage. He was from California, and regularly made us practice earthquake drills (because there are so many earthquakes in northern Germany...).
She remembered that he did many of the zany things others only thought about, and recalled the time we build the igloo.
Apparently, he had been planning that for a while, waiting for the right day with the right snow; he also arranged with the teachers to have them essentially give us the day off and he'd take care of us.
I didn't notice any of that at the time, except that I remember wondering at one point whether the bell for the end of recess shouldn't have rung by then.
A number of teachers and older students started building an igloo out of snow blocks they had rolled together out of the snow. Anyone who wanted to watch them had to "pay" with a snow block they made themself; that kept the number of gawkers down and made the igloo progress more quickly.
When it was done, we took turns going inside. I remember a teacher got a thermometer and measured the temperature outside and inside; when it was my turn to go in, I remember it was rather hot in there. They ended up making a hole or two in the wall for some ventilation and air cooling.
We stayed out there for hours, first watching the igloo being built and then taking turns inside.
Ah, good times, good times.
When I left yesterday, I bought an ISH-branded USB stick and a blue polo shirt with a yellow ISH logo. Stella said, "But you never wear polo shirts!" We shall see.