Additional sub-menu

[WPHarry]

Hi,
I am using this WP-theme on my website. I like it very much and I would like to add a submenu to my existing menu based on categories as can be seen on this website : http://creativecultureint.com/our-work/#category_id_222

Any ideas how that can be achieved ? Is there a widget available ? Plugins ?

Thanks for your you ideas !