The U.S. State Department files travel information and warnings for all countries, world wide. Their annually updated pages contain a short description of the country and useful information about safety, crime rate, health services and insurance. Aimed at U.S. citizens, but useful for anybody. Go directly to their Eritrea Page . You won't find too much information, but they have detailed maps of the country.
Guides exist to all countries.
You might want to go to their Africa Page . Also a German entry . Texts and graphics may be reproduced freely, under the condition that their origin is clearly referred to, see Conditions .