Puzzle - Which is at the Middle

There is a linked list (you can assume that it is unidirectional or bi-directional). The list is not ordered in any specific format (unsorted).

• What are the methods (or ways) by which you find the middle element of the list? (For example, if the element has 11 elements, 6th element is the middle. If you have 10 elements, 5th or 6th (whichever you like) is the middle element of the list).
• What is algorithmic complexity of each method?