The Puppeteer's Den is a building located in the Northwest part of the Sand Village, next to the Sand Graveyard. Inside of the house you can find the Puppet Master.
Currently this is the place where you can obtain Puppet Summoning Technique scrolls. They act as a normal animal summon, you can have both in your Jutsu inventory but you can only 1 out at any time.
To obtain a Puppet Summon you need 1 Summoning Contract which you can obtain at the Sand Village Scroll shop. There are currently 6 different puppets: Fire, Poison, Lighting, Wind, Earth, Water.