A couple things.  First, your function names need to be prefixed with something unique.  WordPress is a big ecosystem, and someone else has probably used all the generic function names you can think of.

Second, `add_rewrite_endpoint` takes care of adding query variables for you. So you don't need this:

    add_filter( 'query_vars', 'add_query_vars');
    function add_query_vars($vars){
        $vars[] = "tours";
        $vars[] = "activities";
        return $vars;
    }

Flushing rewrite rules on every load is not a good idea.  This only needs to be done once after your rules have been added.  Like on plugin activation.  So you `add_endpoints` function could be shorted to this (with a better function name per point one above).

    <?php
    add_action('init', 'wpse42279_add_endpoints');
    function wpse42279_add_endpoints()
    {
        add_rewrite_endpoint('tours', EP_PERMALINK);
        add_rewrite_endpoint('activities', EP_PERMALINK);
    }

Which works fine for posts.  If you want it to work on pages or any other hierarchical post type, you'll have to use the `EP_PAGES` endpoint mask.

    <?php
    add_action('init', 'wpse42279_add_endpoints');
    function wpse42279_add_endpoints()
    {
        add_rewrite_endpoint('tours', EP_PAGES);
        add_rewrite_endpoint('activities', EP_PAGES);
    }

But that's still not going to work as expected for you. Endpoints set their query variable equal to whatever comes after it.  So if your URL is...

    yoursite.com/some-country/some-city/activities/asdf

the query variable activities will be asdf.  If nothing follows `activities`, your query var will be empty (but set), so it will always evaluate as false when you try to catch it...

    <?php
    add_action( 'template_redirect', 'wpse42279_catch_vars' );
    function wpse42279_catch_vars()
    {
        if( get_query_var( 'tours' ) )
        {
            // do stuff!
            exit();
        }
    }

You can get around this by filtering `request` and changing the value of your tours and activities variables to true if they are set.

    <?php
    add_filter( 'request', 'wpse42279_filter_request' );
    function wpse42279_filter_request( $vars )
    {
        if( isset( $vars['tours'] ) ) $vars['tours'] = true;
        if( isset( $vars['activities'] ) ) $vars['activities'] = true;
        return $vars;
    }

You should have a look at this [guide to the Rewrite API][1] I wrote.  The relevant parts for your question are summed up above, however.


  [1]: http://pmg.co/a-mostly-complete-guide-to-the-wordpress-rewrite-api