Hi Jake WM,
As the title says, I have an urge to go on a long retreat mainly to move on from the dark night and get stream entry.
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I am 100% sure that I am dicking around the stages of the dark night. I started a thread a while ago with the reason why I believe I have crossed the A&P and am currently in the dn stages. I can clarify this further if necessary.
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Other than the feeling I have for needing to go on retreat, I have noticed on these forums that many people go on retreat early on in their quests. It has proven beneficial and further backs up my motivation to go on retreat as well.
Adding to this thread for anyone who's reading ~ here's a sort of standard cautionary note: retreat centers, lay and monastic, can be chock full of other people (again, lay and monastic) who are also dwelling in the "dukkha nanas", even the person who has been designated (by you or others) as "the teacher" or whoever has designated themselves "the teacher", paid or free. Even a teacher with a touted reputation can be teaching from, say, a mind of arrogance, promoting its own expression/views over those of others.
Here are some guidelines for dharma teaching in the Pali tradition, paraphrased, from the
Anguttara Nikaya 5.15 (to Udayi, transl. Thanissaro, reprinted AccesstoInsight):
A dharma teacher teaches:
1- step-by-step
2- cause and effect (also commonly known as: "continent identity", "inter-being", "co-arising", "dependent origination")
3- with a mind of compassion
4- not for the purpose of material gains (including status)
5- without disparaging self or others
So if one goes on retreat (be it lay-led or monastic), one may have to work hard to be "an island unto oneself," doing chores and all group activities without mixing own-pain with pain-of-others (which pains can appear as depression as much as malice). Three of the brahamviharas (kindness, altruistic joy, compassion) are sane reactive emotional states; equanimity (the fourth brahmavihara) is a deep safe harbor, however it can be mistaken with cool aloofness/conceit/superiority when one is still in dark night terrain.
Maha-parinibbana Sutta (Digha Nikaya 16, translation: Vajira and Story, printed by AccesstoInsight):
33. "Therefore, Ananda, be islands unto yourselves, refuges unto yourselves, seeking no external refuge; with the Dhamma as your island, the Dhamma as your refuge, seeking no other refuge.
"And how, Ananda, is a bhikkhu an island unto himself, a refuge unto himself, seeking no external refuge; with the Dhamma as his island, the Dhamma as his refuge, seeking no other refuge?
34. "When he dwells contemplating the body in the body, earnestly, clearly comprehending, and mindfully, after having overcome desire and sorrow in regard to the world; when he dwells contemplating feelings in feelings, the mind in the mind, and mental objects in mental objects, earnestly, clearly comprehending, and mindfully, after having overcome desire and sorrow in regard to the world, then, truly, he is an island unto himself, a refuge unto himself, seeking no external refuge; having the Dhamma as his island, the Dhamma as his refuge, seeking no other refuge.
35. "Those bhikkhus of mine, Ananda, who now or after I am gone, abide as an island unto themselves, as a refuge unto themselves, seeking no other refuge; having the Dhamma as their island and refuge, seeking no other refuge: it is they who will become the highest, [20] if they have the desire to learn."
One takes up a practice in which own mind is calming, not stressed, and not provoked into the hindrances (ill-will, craving, confusion, doubt, dullness). Nothing esoteric: Just developing the mind into calmness so that it can develop understanding of itself and objects it contacts, including the senses and its own consciousness and others.
Best wishes, retreatants!

[edited: link correction and some grammar]