Group shopping site Groupon is continuing its buying spree, acquiring the parent company of check-in service Whrrl late Monday, dubbed Pelago, which the company said in a blog post it would retire on April 30.

Pelago was one of the first companies backed by Kleiner Perkins Caufield & Byers’ iFund. In its early days, Whrrl seemed overshadowed by Loopt — now, of course, Foursquare is the king of the check-in startups.

Terms of the deal, including the selling price, were not disclosed.

Calling it “great way to start the work week,” Groupon CEO Andrew Mason said that Pelago CEO and former Amazon executive Jeff Holden will be now be overseeing product development at Groupon.

The rest of the Seattle-based Pelago group will be wrapped into the daily deal site’s “Grouponnovations.”

Its acquisition is a good fit for Groupon, said Mason, because the two companies share the same “anti-search philosophy.

Wrote Mason:

We’ve always liked CEO Jeff Holden, the Whrrl team and the technology they’ve developed. Their obsession with real-world serendipitous discovery, or “Anti-Search,” is core to Groupon’s mission. It’s about discovering what you didn’t know you didn’t know, right in your own backyard. Jeff intimately gets consumer buying behavior and the importance of a great user experience, and his team is this awesome combination of data-driven creatives…the people who create smart products that are really fun to use.

Groupon has made a number of high-profile buy-ups in recent months, including grabbing Indonesia daily couponing company Disdus.

It also launched Groupon Philippines, Hong Kong, Taiwan and Singapore through the acquisition of daily deal sites: Beeconomic (Singapore and Philippines), uBuyiBuy (Hong Kong) and Atlaspost (Taiwan).

At the time of its buyout, Pelago had over $22 million in funding from Kleiner Perkins, Reliance, Bezos Expeditions, T-Ventures, DAG Ventures and Trilogy Equity Partners.