When looking at your page source the title tag is formed wrong.
<Aan de Maas>Restaurant Aan de Maas Kerkdriel</title>
Should be <title>Restaurant Aan de Maas Kerkdriel</title>
the header image has no alt text.
<img src="https://www.aandemaas.eu/wp-content/uploads/header5.jpg" alt="" />
Andyour sliding image menu have slidingdoor as the text and no alt tags.
<div id="imageMenu">
<ul>
<li class="bk0"><a href="https://aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/1.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk1"><a href="https://www.aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/2.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk2"><a href="https://www.aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/3.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk3"><a href="https://aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/4.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk4"><a href="https://aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/5.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk5"><a href="https://aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/6.jpg') repeat scroll 0%;">slidingdoor</a></li>
<li class="bk6"><a href="https://aandemaas.eu" style="background: url('https://www.aandemaas.eu/wp-content/themes/sliding-door/imagemenu/images/7.jpg') repeat scroll 0%;">slidingdoor</a></li>
</ul>
</div>