The Wisconsin glaciation (also known as the Devensian, Midlandian, Würm, and Weichsel glaciation in different areas around the world) was the last Ice Age, during which glaciers extended as far south as modern-day California, New York, France, Germany, and Poland. Most of Europe was either frozen solid or steppe-tundra, much as Siberia is today.
The Wisconsin glacial advance began about 70,000 years ago, reaching its maximum extent 18,000 years ago, before receding. Although there were numerous Ice Ages throughout the last few million years, the Wisconsin glaciation is what is usually being referred to when people say "Ice Age," because it is the most recent, sculpted many modern geological features (particularly in the Northern hemisphere), and affected human evolution and culture the most.
Because of successive glaciations, it is sometimes difficult to determine exactly which Ice Age had an effect on which geological feature, but thorough investigation has largely been able to piece it together. There are numerous valleys in North America, Europe, and Asia known to have been shaped by glaciation. These often feature large exposed areas of granite, sliced and ground by the immense pressure of ancient glaciers.
The Baltic Sea, in Northern Europe, was created entirely as a side effect of the Wisconsin glaciation, a product of melting glaciers. This is why the Baltic Sea is the largest sea in the world filled with brackish water, and its bottom was sculpted by glacial erosion. "Brackish" means the water is saltier than fresh water, but less salty than the oceans. The Baltic Sea is highly unusual is that its surface water is fresh, but its deep water is salty, and difference species occupy each layer.
During the Wisconsin glaciation, humans survived in the frozen areas by wearing animal pelts and taking advantage of fire as much as possible. Like Eskimos today, humans are capable of adapting to extremely cold environments, and had the basic technology to do so. Metalworking had not been developed yet, so flint was the main raw material for industry. Homo sapiens moved into the frozen regions about 40,000 years ago, when we colonized Eurasia and Oceania. Humans lived alongside Neanderthals for about 15,000 years, until the latter went extinct 33,000 to 24,000 years ago. Humans may be responsible for this extinction.