Generate a one-path maze
Jelly, 36 35 34 33 32 bytes

2*×5H_2Bị⁾ |
_3”-ẋ”+;;Çsẋ2U3¦ṁµY


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Builds a nighter™ the other way around to the examples like:

+---- |
|     |
| ----+
|     |
+---- |
|     |
| ----+


How?

2*×5H_2Bị⁾ | - Link 1, pipes &amp; spaces: n      e.g. 7
2*           - 2 raised to the nth power      e.g. 128
  ×5         - multiply by 5                  e.g. 640
    H        - halve                          e.g. 320
     _2      - subtract 2                     e.g. 318
       B     - convert to binary              e.g. [1,0,0,1,1,1,1,1,0]
        ị    - index into (1-based)
         ⁾ | - char list " |"                 e.g. " ||     |"

_3”-ẋ”+;;Çsẋ2U3¦ṁµY - Main link: n            e.g. 7
_3                  - n - 3                   e.g. 4
  ”-                - char list "-"
    ẋ               - repeat                  e.g. "----"
     ”+             - char list "+"
       ;            - concatenate             e.g. "+----"
         Ç          - call last link (1) as a monad
        ;           - concatenate             e.g. "+---- ||     |"" 
          s         - split into chunks of n  e.g. ["+---- |","|     |"]
           ẋ2       - repeat 2 times          e.g. ["+---- |",
                                                    "|     |",
                                              +--&gt;  "+---- |",
                                              |     "|     |"]
              3¦    - apply to index 3:       |
             U      -    upend                +---  "| ----+"
                ṁ   - mould like n (i.e. repeat to fill)
                 µ  - monadic chain separation
                  Y - join with line feeds


(each byte saved involved fairly non-trivial changes, see the edit history if you're interested, although I just noticed that Link 1 is the same byte count as the more conventional repeat and join: _2⁶ẋ“ ||“|”j)