http://whirtorrgetftvz4g466sjqkegtyi35bjl4bvotfkfossunf5my4x6ad.onion/blog/bitcoin-tumbler
The tumbler then sends 1 BTC from the mixed pool to Bob's address. Bob receives 1 BTC in his address, but he has no idea that it came from Alice or anyone else. Alice's original 1 BTC is now mixed with other Bitcoin in the pool, making it much harder to trace back to her.