"Bentley View" is the free software you want ....BUT...
You need to get someone who is a registered Microstation software owner to get you code to use "Bently View".
The logic is ...
You'll be getting DGN files from a legal user of MicroStation, therefore he/ she can get the code via email by registering for the viewer.
Then you download it and they give you their registered code.
Then the viewer is yours.
Sorry!