Nancy, yes, sea level is basically when there is no elevation at all and the ground is at the same level as the shoreline. For example, Denver is in mountainous terrain and is actually 1,615 meters above sea level. If you're used to living at sea level, the oxygen can feel really thin when you go to place like Denver. I was in Denver for a conference and it was funny to hear so many other out-of-towners whining about the oxygen (I'm from ABQ, NM which is at the same altitude as Denver so I was doing fine.)
How very cool that you know how to ice-skate! I've never known how to even roller-skate, let alone ice-skate, but it looks wonderful in the figure skating events for the Winter Olympics. I know what you mean about not trusting the ice on the river or lake. That would make me very nervous. And I've heard about those little houses that the ice-fishermen use. We get that in Minnesota and places up around the Canadian border in winter. I've heard some of those little houses can be quite nice to stay in with heat and protected from the wind while someone's sitting there fishing through the ice.