A Tunisian citizen can enter Morocco or Algeria without a visa. But what is the position if they wish to enter Ceuta or Melilla, crossing the border from Morocco? Do they need to apply for a Schengen visa?
Ceuta and Melilla are administered by Spain (though Morocco disputes their sovereignty over the cities). Both countries maintain border controls at the borders and Spain has built border fences around both cities.
Residents of the Moroccan provinces of Tetuan and Nador have a special local border crossing scheme whereby they can enter these cities without a visa (but they cannot enter mainland Spain or the rest of the Schengen area). Moroccan nationals living in other provinces can obtain a limited territorial validity visa from Spain for those cities only.
(b) The specific arrangements for visa exemptions for local border traffic between Ceuta and Melilla and the Moroccan provinces of Tetuan and Nador shall continue to apply.
(c) Moroccan nationals who are not resident in the provinces of Tetuan or Nador and who wish to enter the territory of the towns of Ceuta and Melilla exclusively shall remain subject to the visa requirement. The validity of these visas shall be limited to these two towns and may permit multiple entries and exits ("visado limitado múltiple") in accordance with the provisions of Article 10(3) and Article 11(1)(a) of the 1990 Convention.
Notably, while the cities are part of the Schengen area, there are passport checks upon departure by air or ferry, in order to ensure that Moroccan visitors without visas and illegal immigrants cannot migrate to Europe or elsewhere.
(e) Pursuant to its national law and in order to verify whether passengers still satisfy the conditions laid down in Article 5 of the 1990 Convention on the basis which they were authorised to enter national territory upon passport control at the external border, Spain shall maintain checks (on identity and documents) on sea and air connections departing from Ceuta and Melilla and having as their sole destination any other place on Spanish territory.
To the same end, Spain shall maintain checks on internal flights and on regular ferry connections departing from the towns of Ceuta and Melilla to a destination in another State party to the Convention.
There's no provision that I can find for Tunisian nationals, so it appears that you will need a regular Schengen visa.