Since the multi-tag search off Last.fm Playground is not working or otherwise, shut down, I found a solution to multi-tag searching in a DIY fashion. It's ridiculously easy. 

Here's a few things you will need to do.

Use Google. 

1.Go to http://www.google.com/

2. Do the following by copypasting this into the google search:  www.last.fm/music intitle:"tags for" "insert tag" secondary tag

Example: www.last.fm/music intitle:"tags for" "post-rock" shoegaze

3. Happy multi-tag searching!