TL;DR:
Cultures have deep, often invisible layers that shape who people are and how they see the world. Like an iceberg, only a small portion of culture—behaviors and customs—is visible, while the vast majority—beliefs, values, and assumptions—lies hidden below the surface. Other analogies, including concentric circles and an onion, have also been used to explain culture. Recognizing these layers and metaphors can encourage deeper cross-cultural understanding.
Culture is more closely connected to our sense of identity and self-understanding than we often imagine. What we can readily see and understand of a culture—whether our own or another—is comparable to the visible portion of an iceberg.
Although we know that only a small portion of an iceberg is visible above the water, it can still be difficult to imagine how much lies beneath the surface. Approximately 90% of an iceberg lies below the water's surface. Similarly, many cultural elements, including beliefs, values, and underlying assumptions, lie hidden beneath the surface. We may not even be aware of how deeply our culture shapes our values and influences our view of life, our interpersonal relationships, and other aspects of daily life. The iceberg analogy for culture has been attributed to Edward T. Hall, although that attribution has not been verified.
A concentric circle diagram illustrates how worldview is foundational to beliefs, how beliefs are foundational to values, and how values prompt behavior. Lloyd Kwast describes culture as a series of successive layers through which one moves from observable behavior toward its underlying heart. He explains that cultural values are not selected arbitrarily; rather, they reflect an underlying system of beliefs. At the heart of a culture is its worldview. Kwast cautions that people who share the gospel cross-culturally may see little genuine change if they fail to consider that worldview.

Diagram and quotes are taken from "Understanding Culture" by Lloyd Kwast, published in the second edition of Perspectives on the World Christian Movement, © by William Carey Library
To be sure, Lloyd Kwast's model of culture is, as Kwast himself admits, "far too simple to explain the multitude of complex components and relationships that exist in every culture." However, it can be a useful starting point.
The image of an onion is often used to describe the different layers of culture. The outer layers are the artifacts and products as well as patterns of behavior. The next layers hold the beliefs, norms, and attitudes of that culture. The middle or core of the onion contains the underlying cultural assumptions and values.
Geert Hofstede created the Cultural Onion model, which depicts culture as layers surrounding a core. The core represents a culture's values, which tend to change slowly. Even when a value appears outdated, it may continue to influence people subconsciously. The first layer around the core consists of rituals or practices embedded in that culture. Those rituals change only slowly. Another layer contains the "heroes," who may be real or fictional people. They both reflect and influence the beliefs, norms, and attitudes of that culture. On the outside are the symbols and practices that are currently fashionable within the culture. The outer layers can be modified, retrained, and relearned. The core—the culture's inner values and assumptions—is different.
—Howard Culbertson, hculbert@snu.edu
To capture the richness of what we mean by culture, that concept has been described using a variety of analogies. Here are seven more of them:
This collection of analogies offers a variety of ways for us to think about the dynamic complexity of culture. Each analogy or metaphor brings out something important. Together, these analogies can help us see how our culture influences us as individuals and as societies.