Hash#deep_traverse extends Ruby's Hash class with a method yielding pairs consisting of path and value. Each path consists of a list of keys leading to the last, right-most key.

hash_deep_traverse.rb

class Hash
  def deep_traverse(&block)
    stack = self.map{ |k,v| [ [k], v ] }
    while not stack.empty?
      key, value = stack.pop
      yield(key, value)
      if value.is_a? Hash
        value.each{ |k,v| stack.push [ key.dup << k, v ] }
      end
    end
  end
end

# d = {:a=>{:b=>{:c=>1}, :d=>2}}
# d.deep_traverse{ |path,value| p [ path, value ] }
# => [[:a], {:b=>{:c=>1}, :d=>2}]
#    [[:a, :d], 2]
#    [[:a, :b], {:c=>1}]
#    [[:a, :b, :c], 1]