No! solo travelers are not allowed to take the Nar Phu Valley Trek or any restricted area treks in Nepal. Nepal's government does not give permits for solo travelers in restricted areas. These permits require at least two trekkers and a government-registered guide.  In the case that you are only one person, but would still like to do this trek with a registered guide, you can pay the other ‘ghost permit,’ as if there was another trekker with you. It is doable but would cost you double the permit fee.  We hope our government will change the policy soon, so more people can discover the beauty of the Nar Phu Valley, but until then, you must travel with a group of two people and a registered local guide.