I am not sure since which version (maybe 16.04). The Unity shortcut for navigating workspace became quite stupid. Moving to the workspace on the left and right use ctrl-alt-left and ctrl-alt-right and moving to the workspace above and below use something ctrl-super-up and ctrl-super-down instead. In earlier versions, I think the default were ctrl-alt-up and ctrl-alt-down for the latter. One can change this though under setting->keyboard->shortcuts->navigation.
Update:
Install unity-tweak-tool to configure workspace