What kind of memory it is?
The travel experience etc, are episodic memories. The duration of these memories mostly depend on emotion and novelty.

The typing and singing, are procedural memories. They are formed with practice. Repetition and consistency are the two most important factors for this type of memory. We do not have any conscious access to procedural memory, we simply perform what we know. 

The PIN memory can be explained with cued recall. The image of the post office is associated with the PIN, so whenever you imagine the post office the PIN number is also activated.