All of the castle views can be found in the Castle View menu. Below each castle view is a screenshot of that specific game view - you can exit any of these views at any time simply by either left or right clicking with your mouse. You get to the menu below when you click on the eye icon in the left sidebar below:
|Architects View||View Inside the Keep||Lord's Eye View||Gatehouse Views||Free View||View over the Granary|
Architect view (more commonly know as a bird's eye view, or overhead view) is useful when placing buildings and can help to spot any potential gaps in the building construction. You can also activate or deactivate this game view by pressing the spacebar.
The view inside the Keep. It will only generally display this from one angle.
This is the view from the top of your Keep, where the Lord is usually stationed.
The Gatehouse view selects a single Gatehouse (seemingly at random) and provides the view over it whenever you click this icon. If you don't have at least one gatehouse built, this view will be unavailable and nothing will happen when you select the icon.
Free View is probably the most useful view of all - you can move practically anywhere on the entire map in any way and you can view the map from any angle.
This will provide a view over the granary, which is useful if you have a lot of buildings nearby it and can't see very well.