Most people who want a retreat never go on one, because a retreat means a place, a fee, a weekend and a plane. The parts that actually do the work are smaller than that, and none of them require leaving the house.
What is actually doing the work
Strip a retreat down and three things are left. A length of time long enough that you stop checking it. A boundary at each end, so it begins and finishes rather than dissolving. And an agreement with yourself about what happens inside, made in advance, so you are not negotiating while you are in it.
The mountain view is lovely. It is not the mechanism.
What a retreat gives you is not scenery. It is a block of time nobody else has a claim on.
Three hours, arranged
An afternoon divides naturally into arriving, working and returning. The first half hour is for landing: tidying the surface in front of you, making something to drink, letting the noise of the morning settle. Nothing important happens here and it is not wasted time.
The middle is the work, whatever you chose it to be: writing, reading one thing slowly, sitting with a question. The last half hour is for coming back out, which most people skip and then wonder why the afternoon evaporates the moment it ends.
Deciding before you begin
The single largest failure is arriving at a free afternoon with no plan and spending it deciding. Choose the question the day before. One question, written down, is enough structure to keep three hours from drifting.
The second largest failure is ambition. An afternoon is not long enough to resolve your life, and setting out to do so guarantees the feeling of having failed at rest, which is a strange and unnecessary way to end a Sunday.
Marking the edges
Do something small and deliberate at the start and at the end. Light is traditional; so is a particular chair, or a particular cup, or writing the date at the top of a page. It sounds ceremonial because it is, and the ceremony is doing real work: it tells the mind that this block is different from the hours on either side of it.
Without edges an afternoon of rest becomes an afternoon that was not anything, and you will not remember it by Wednesday.