Where does one go?

The tathagata-garbha. The Buddha heart.

The Buddha taught that all beings are Buddhas, but that this is obscured by temporary defilements and obscurations. Just as a treasure buried under the earth, or a precious statue wrapped in a dirty cloth, once the obscuring factors are removed the treasure can be enjoyed in all its splendor.

But what is this Buddha heart and how can we come to experience it?

The Buddha taught many different vehicles by which we can actualize and realize this Buddha heart. The Mahayana sutras describe the tathagata-garbha as a seed or potential, which we can cultivate and nourish until it becomes manifest and bears fruit. The Vajrayana, or resultant vehicle, describes the tathagata-garbha as being fully manifest since beginningless time, but obscured and unrecognized. The Vajrayana employs various skillful means to try to purify and remove these obscurations. Within the Vajrayana vehicle, the highest understanding of the tathagata-garbha is understood within the Dzogchen tradition.

Dzogchen, or the Great Perfection, describes the tathagata-garbha as being timelessly liberated. There is nothing to change, manipulate or improve. The true nature of reality is perfect just as it is, there is nothing to purify, nothing to cultivate, nothing to attain. Failing to recognize this true nature, we wander in and out of various mental states. Recognizing this, one is primordially free.

Where does one go when they have actualized the tathagata-garbha?

Tathagata is a name for the Buddha, which means 'One who has thus gone', 'Beyond coming and going' or "One who has gone to the true nature'. Garbha means heart, essence or womb. So one who has actualized the tathagata-garbha is the 'heart of one who has gone beyond', or the 'heart of one who has gone to the true nature'.

The tathagata-garbha is beyond mind. It is not the coming and goings of our mind. It is not an idea or a projection of what should be. It is not a belief or a philosophy. It is not 'in your head'. Awakening isn't in your head- its embodied, manifest.

The practitioner of Dzogchen is introduced directly to awareness beyond mind. The are introduced to the timelessly liberated natural state of being. Once introduced to this unique state, the practitioner clarifies doubt and uncertainty about this unique state, until they have truly gone beyond to the true nature. Then, they can continue with confidence in liberation. As Garab Dorje wrote in his Three Words that Strike the Essential Point: 

One is introduced directly to one's true nature,
Be decisive about this unique state,
Continue directly with confidence in liberation.

Or as Garab Dorje also states:

Mind's nature is and always has been Buddha,
it is neither born nor ceases, like space.
When you realize the authentic meaning of the equality of all things,
To remain in that state without effort is meditation.