De or het morgenwandeling?

The correct Dutch article is:

de morgenwandeling

Rule Words ending in -ing: almost always de. See the rule

How to use morgenwandeling

the morgenwandelingde morgenwandeling
this morgenwandelingdeze morgenwandeling
that morgenwandelingdie morgenwandeling
our morgenwandelingonze morgenwandeling
your morgenwandelingjouw morgenwandeling
every morgenwandelingelke morgenwandeling
which morgenwandeling?welke morgenwandeling?
a big morgenwandeling / the big morgenwandelingeen grote morgenwandeling, de grote morgenwandeling