What is a Mish?ol Keramim?
Rashi (citing Targum Onkelos): ?A pathway 1 through the vineyards?.
Targum Yonasan: ?In the middle of the vineyards.
Where one walks on foot ? as in Yeshayah, 40:12 and Melachim 1, 20:11 (Rashi).
What is a Geder?
Rashi: A Geder is a stone wall. 1
Targum Yonasan: In this context, it refers to the pile of stones and the monument that Ya'akov and Lavan erected 2 with a mutual agreement 3 never to pass them in order to do harm to the other. 4
Which explains why it caused Bil'am to become lame. Refer to 22:25:1:1. See also Oznayim la'Torah, who equates Rashi with answer #2.
See Vayeitzei Bereishis, 31:51-52.
Targum Yonasan: Which Bil'am ? alias Lavan, had just abrogated.
Having delegated the pile of stones and the monument as witnesses (Vayeitzei, Ibid.), the witnesses were now punishing him - as the Torah states in Shoftim Devarim, 17:7.