Thread

{exp:query sql="SELECT cat_id FROM exp_categories WHERE cat_url_title = '{segment_2_or_whatever}' LIMIT 1"}
    
    {exp:channel:entries
        channel="your_channel"
        disable="categories|category_fields|member_data|pagination|trackbacks"
        dynamic="off"
        category="{cat_id}"
    }
        
        ... other awesome code here ...
                    
    {/exp:channel:entries}
    
    {if no_results}
        That is not a valid category.
    {/if}
    
{/exp:query}

{if segment_2_category_id == ""}
  {redirect="404"}
{/if}