Using a checklist to search against metadata

Have you looked into the shortcode API? It has some very powerful tools to add as many array items as you’d like, and put the shortcode anywhere on your site.

Here is a small demo of what you could do:

function create_shortcode( $atts, $content = null ) {
     $a = shortcode_atts( array(
           'sauna' => 'attribute1',
           'parking' => 'attribute 2 default',
           'natural' => 'attribute 2 default',
           'food' => 'attribute 2 default'
   ), $atts );

    foreach ( $a as $key => $value ) {
         echo '<input type="checkbox" value="' . esc_attr($key) . '"' . $key. '>' . $value . "<br>";
    }

  }

add_shortcode( 'japan', 'create_shortcode');

Now to utilize this shortcode just enter this text [japan class="headline"]asdf[/japan] and it will produce a column of checkboxes. Not pretty but should get you in the right direction.