Sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum, that can be dissolved naturally by circulating ground water. Sinkholes also occur in sandstone and quartzite terrains. As the rock dissolves,
A Void constraint to the original, avoiding the most commonly used letter of the alphabet. This precludes the use of words normally considered essential such as "je" ("I"), "et" ("and") and "le" (masculine "the") in French, as well as "me," "be," and "the" in English. The Spanish version contains no "a", which is the second most commonly used letter in the Spanish language (first being "e"), while the Russian version contains no о. The Japanese version does not use い ("i") at all. "A Void"'s plot follows a group of individuals looking for a missing companion, Anton Vowl. It is in part