Text adventure and global variables
It will make sense to use OOP in your implementation.
You can model the crypt as a Crypt class,
there gate and lever can be attributes,
and entrance, lever_room can be methods.

Transforming your implementation is quite easy, follow this pattern:

class Crypt(object):
    def __init__(self):
        self.gate = False
        self.lever = False

    def entrance(self):
        while True:
            choice = raw_input('&gt; ')

            if choice == 'west':
                self.guard_shack()
            elif choice == 'east':
                self.lever_rm()
            elif choice == 'north' and not self.gate:
                print "The gate is still closed and locked."
                self.entrance()
            elif choice == 'north' and self.gate:
                self.fountain_rm()
            else:
                self.entrance()

# ...

def main():
    crypt = Crypt()
    crypt.welcome()
    crypt.entrance()


To learn more about classes and OOP in Python,
I recommend the official tutorial.



It's not a good practice to run code in the global namespace,
because if you try to import this module from another module,
all that code will be executed immediately.

The right way to do this in Python is to add this conditional:    

if __name__ == '__main__':
    main()


This condition will only be true when the file is executed as a Python script.



Don't use the == operator to check the value of boolean variables and expressions like this:


elif choice == 'north' and gate == False:
    print "The gate is still closed and locked."
    entrance()
elif choice == 'north' and gate == True:
    fountain_rm()



Instead of x == True you can use the boolean variable directly,
in case of x != False you should use not x, for example:

elif choice == 'north' and not gate:
    print "The gate is still closed and locked."
    entrance()
elif choice == 'north' and gate:
    fountain_rm()




This looks like a bug:


else:
    entrance(gate)



Because in your declaration the entrance method doesn't take any parameters.