Some countries will require a consent letter signed by your parents or guardians and some may refuse your entry all together. Most hotels will make you jump through extra hoops as a minor or may not let you stay there at all. Some tourist attractions won’t let minors in without an adult accompanying you. You’ll be all alone. If you’re have a medical emergency, are arrested, or experience any other kind of pitfall, you may not be able to reach anyone back home.
In some countries, like Portugal, minors must have a letter signed by both of their parents, and must authenticate that letter at an embassy prior to travelling. In other countries, like Spain, minors can generally travel alone, but if they are arrested, end up in the hospital, or otherwise run into problems, they may be held by authorities until their situation can be resolved.
If the city you plan to visit has a youth hostel, try calling them. Many youth hostels will allow minors to stay, although most are restricted to those 16 and older.
