If you are trapped in American and unable to get abroad, there are still some great ways to have a little mini vacation before it starts to get too cold.
The Appalachian Trail is VERY long and extends nearly the entire east coast. There are many that actually hike the entire thing but this is probably too much of an undertaking for most people. However, there are tons of access points and at many of the locations there is plenty to see without doing the entire 2200 miles of it which extends all the way from Georgia to Maine.
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Just like the sign indicates, it takes most people 6 months to do the entire thing and if you have a job or a family, obviously this isn't something you can just go and do. But like it says, 3000 people a year do the entire thing each year, which is a bit crazy if you ask me and also a test of will. However, if you are an outdoorsy type of person and can deal with a tent and the unknown, I would imagine this could be a fantastic and relatively safe way to do some sort of extreme trekking.
I say "safe" because it's not like you are not going to encounter other people since there are a ton of attractions along the way and even though they are unlikely to be doing the entire thing they are likely visiting the local sites and you are probably never very far from a parking lot of some sort and there is mobile service from end to end. The likelihood of you just being injured and stranded is pretty slim.
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Along the way there are of course amazing views throughout because you are, for the most part, in the mountains most of the time. This isn't the sort of elevation that you would get to see in the Rockies or somewhere like Everest or K-2, but it's still pretty amazing, especially in the fall when the leaves change color.
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If you are a fan of waterfalls, and I don't know anyone who isn't, you are in for a treat in most of the states that the Trail runs through and I personally have the most experience with the falls that are in Virginia.
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Unfortunately, many of the areas in states that are more nervous about Covid than others they have closed the trail access, but I personally know people who simply jump the fence. It isn't like there is anyone there guarding it or anything because at the end of the day it is just one very long national park and the people I know that "go anyway" have not gotten in trouble for it. It's not like they are going to patrol a 2000 mile long trail checking to see if people are wearing masks.
There's a pretty funny story about two people who completed the entire trail despite being specifically told to not undertake it by authorities and they have some pretty great stories about defying orders and dodging cops that were easily spotted and avoided during their trip for several months. At certain points one of the hikers went very far off trail in order to evade police and park rangers.
That story can be seen here if you want to see what a real definition of hiking determination looks like.
I'm not trying to encourage anyone to break the law but if you are on the East Coast and are desperate to have something to do it might not be a terrible idea to have a look online to see if your access to the park is open or not. Things vary from state-to-state and all of these places except in the southern reaches are soon to be too cold to take part in without specialized gear of some sort.
It is probably already dangerously cold in the Northern-most parts of the trail. I've only been up to Maine a few times in my life and while it is lovely, the winter starts entirely too early up there for my liking :)