You can do walk throughs in Revit, and by exporting to DWF and viewing it in the free AutoDesk Design Review software.
But Navisworks has more control over walk throughs so it may be worth importing your Revit model into the free Navisworks viewer.
A bit of skill is needed to make it look easy. I strongly suggest you practice before embarrassing yourself in front of other people.
You first need either a 3D DWFx file or a Navisworks .NWC file.
You need the NWC exporter installed to create a .NWC.
Refer to EXPORTING for NAVISWORKS on how to create an .NWC file.
NWC is best but you don't have the exporter export a 3D DWFx from Revit:
Go to, or create, a 3D view that only displays what you want to export.
While in that view from the purple R top left, select Export > DWFx.
Name and save the file.
Exit Revit.
You will need Navisworks freedom which is free software from Autodesk at:
http://usa.autodesk.com/adsk/servlet/pc/item?siteID=123112&id=11091608
Open up NavisWorks select the Giant N and press Open
Browse to the DWF and select it and press open
Once the DWF opens in NavisWorks you can use the view cube to rotate around the 3D model
If you like to go on a walk through in the building select the Viewpoint tab then select the Realism drop down menu and tick Third person box after that press the Walk function.
Now use the mouse to navigate the avatar you will notice that you are floating of the ground
What you will have to do is go to the Viewpoint tab again select the realism drop down menu and select Collision Gravity & Crouch.
Once those three tick boxes are checked if you continue to walk using the mouse or the arrow keys you will come down to the air to the surface
Now you are free to walk around on the ground. While you’re walking use the middle wheel button on the mouse if you want to look or up and down.
If you come to a door or entry point and you want to go inside the building you will have to turn off Collision so you can walk through it. Turn it back one once you’re in the room you wanted to enter.
Also note you can change your avatar select the Viewpoint tab à camera button à settings button then from the drop down menu select the avatar you wish to be.