code: def add_mountains(self):
          
          from noise import pnoise2
          import random
          random.seed()
          octaves = (random.random() * 0.5) + 0.5
          freq = 17.0 * octaves  # 
          for y in range(self.grd.grid_height - 1):
              for x in range(self.grd.grid_width - 1):
                  pixel = self.grd.get_tile(y,x)
                  if pixel == 'X':     # denoise blocks of mountains
                      n = int(pnoise2(x/freq, y / freq, 1)*11+5)
                      if n < 1:
                          self.grd.set_tile(y, x, '#')
docs: instead of the add_blocks function which was to produce
          line shaped walls for blocking path finding agents, this
          function creates more natural looking blocking areas like
          mountains