Three things:
The essence/energies distinction, more specifically, St. Gregory the Theologian saying that contemplating the uncreated essence of God leads to madness. I used to be terrified trying to contemplate eternity in my youth, starting at 7 or 8. If I thought about it perchance I would lie awake in pure terror until I could divert my mind by thinking about other things. Because the idea of either existing forever or dying terrified me, and so I was a Christian but scared of Heaven as much as Hell and as much as death and annihilation itself. While I was at Disneyland I had nightmarish thoughts while waiting in line for Pirates of the Carribean, about what could have created God. But the cheery organ music from Swiss Family Robinsons Treehouse distracted me. But that night on the two hour drive home I reclined in the family car in silent terror. So when I read St. Gregory on this point, it was like the weight of a thousand elephants had been lifted from my shoulders.
Secondly, apophatic theology. Contemplating God by means of the via negativa, in conjunction with the Jesus Prayer, reliably produces a certain euphoria. I avoid this as a matter of course however and focus on the Jesus Prayer itself because I feel I am unworthy to gaze upon the Throne of God through the vista apophatic theology affords while I am still so much a slave to my passions, and could easily fall into prelest. But if I am able to be a better Orthodox Christian then I might dare to pursue this further, under the watchful eye or my father/confessor, who right now is too busy with people in the parish distressed about the situation in the Middle East to be my mystical babysitter. But there is a good monk at St. Anthonys who I have a rapport with and I think when conditions permit I will spend time with him on this.
Thirdly, and most pressingly, the Liturgy. The Divine Liturgy, and the Divine Office and Sacramental services of all Eastern and Oriental Prthodox churches and our close cousins the Assyrians, the Romans and the Anglicans. But most especially the Orthodox, who take the liturgy to the extreme. Its beauty maddens my soul like wine. I love most of all the Syriac, Coptic, Armenian and Church Slavonic approaches. Individual parts from each. The layout of a typical ROCOR parish, and the music. The heart stopping intensity of the Coptic confession. The conceptual elegance of the Armenian services, and the wonderful mystical style they imparted to churches in the Holy Land. And the exquisite way Syriac priests sing the liturgy, not just chanting it but really singing it. The Copts also do this but the Syrian Syriacs, the Suroye, sing it in a mournful quality as opposed to the more cheerful Coptic style and make extensive controlled use of half Romes and quarter tones. But all the liturgies, and not just these four pets of mine, that are Orthodox, contain an intersection of Heaven and Earth and thus even in those which I find stylistically lacking, like my local OCA parish which has a most loving and tender priest and congregation, I find myself able to encounter this reality in some way. So my love for the liturgy is twofold; a love for the superficial aspects which constitute liturgical beauty, and a love for the inner reality that is present even when the luxurious surroundings of a beautiful cathedral church with ornate decor and a splendid choir are absent. I would love to join Fr. Lazarus in celebrating the liturgy in the Cave of St. Anthony, which would be aesthetically unimpressive compared to other services but which would have just as much inner beauty.
I particularly love church services at night, or on Sunday morning. But nighttime services have a special allure. The beauty of Sunday morning is like the major key and the beauty of vespers is like the minor key, or a nighttime Eucharist.