Variants of this question have been asked here on ELL many times (for recent examples, see here, here, here, and here). But I really like how you added this detail, because it helps explain your conundrum:
I am learning past progressive right now and my brain is telling me that it must be different; otherwise, why have simple past and past progressive?
So, let's look at your two sentences:
I was walking to the park.
I walked to the park.
They are both very similar. They both indicate a walk to the park, a walk that happened in the past. In that sense, they don't really "mean" anything different.
So, why have both tenses? That's because of context. Very few English speakers utter simple sentences like "I walked to the park," or, "It was raining," or, "I saw a dog," unless we are answering a question, or telling a story and furnishing additional information. That's why it's so hard to analyze two simple sentences in isolation and figure out some subtle difference in meaning. Taken by themselves, the sentences don't really have a difference in meaning, they just have a difference in how they get used.
Let's imagine a family sitting around a dinner table. Someone asks:
Did anyone walk the dog yesterday?
I might answer:
I walked the dog.
I wouldn't say, "I was walking the dog," because there was nothing else going on, and there's nothing else to say. The dog and I both got our exercise. That's it. Simple past.
However, let's say someone asks a different question:
Is it true that you saw that car accident yesterday? What happened?
Now there's a question that's asking for a story! So, I might begin:
I was walking the dog when I suddenly heard some tires squeal. This old, blue car came
tearing down the street! It careened out of control, and then smashed into three or four
other cars. Glass was shattered everywhere.
In this case, that bit about me walking the dog merely sets up the story. It explains why I happened to be an eyewitness to the dramatic accident. That part would sound very out of place if I used the simple past when describing the walk with the dog:
I walked the dog. Suddenly, I heard some tires squeal. An old, blue car came tearing down the street!
(In fact, that version of the story makes it sound like I may have seen the accident after my walk, not during. It doesn't fit well with the story.)
Of course, there are many different ways I could begin this story, not just one. In fact, I might begin my narrative a bit differently every time I was asked to recount the details:
- I was out walking my dog on the sidewalk when I suddenly heard some tires squeal.
- I was in the middle of my walk with the dog when I suddenly heard some tires squeal.
Notice how I'm sneaking in some additional information with these two versions. The first one indicates that at least some of the streets in my neighborhood have sidewalks. The second one suggests that, if my usual walk is an out-and-back, I was somewhere near my turnaround point when I witnessed the accident.
But don't let those little details get in the way of my main point: When you just look at two sentences – one in the simple past, the other in the past progressive – don't search for some difference in meaning. You'll drive yourself crazy. Instead, try to imagine situations where one would be more appropriate than the other:
Where did you go yesterday?
I walked to the park.
Where were you yesterday, around noon, when I tried to call you?
I was walking to the park.
The sentence as it stands there is not correct.
This is due to the circumstance that to sleep is usually an intransitive verb that does not take an object. With the leading was the construction would be passive voice, but English doesn't use intransitive verbs that way. However, intransitive verbs can use the past continuous and thereby was sleeping.
sleep intransitive verb
to rest in a state of sleep - MW
Admittedly there are transitive uses of sleep, but they do not fit in the construction of the sentence in the question.
The problem with intransitive verbs is that they don't go over into a passive voice. I.e. you can't be slept. If it was a transitive verb that took an object that would easily be understood. Take the transitive verb to slap for example.
I was slapped when he came back to the home.
This sentence offers two explanations at once. Firstly it's homophone to the sentence from the original question. Thus, it might be what was spoken if the question is based on something heard.
Secondly it shows that two past tense verbs can actually be just simple past but in a passive construction.
In the most commonly considered type of passive clause, a form of the verb be (or sometimes get) is used as an auxiliary together with the past participle of a transitive verb; - Wiki: Passive Voice
A transitive verb is a verb that requires one or more objects. This contrasts with intransitive verbs, which do not have objects. Transitivity is traditionally thought of as a global property of a clause, by which activity is transferred from an agent to a patient. - Wiki: Transitive verbs
Best Answer
This is governed by ‘pragmatics’, the knowledge and interest you and your hearers or readers bring to the situation, rather than abstract grammar.
If you were speaking of qualities of the properties which endure into the present, you may use the present tense:
But you are not required to use the present. You do so only if your topic, the matter you are talking about, involves the current status of the properties. If on the other hand your topic is the status at the time of the sale or the transaction itself, you use the past.
When it comes to the price, you are almost obliged to use the past tense: The price was $500,000. Markets change rapidly, so the price is in most circumstances a quality of the transaction, not the properties. If you say the price is $500,000, your hearers will infer that the properties are now being offered for sale again at an asking price of $500,000.