A Schengen Type C tourist visa is generally not extendable. Extensions are only considered in exceptional circumstances, such as a medical emergency or force majeure, where the applicant is genuinely unable to depart within the visa's validity period. Travellers who know in advance that they will need to stay longer than 90 days should apply for a Type D long-stay visa before travelling, rather than attempting an extension after arrival. Overstaying a Schengen visa without proper authorisation can result in entry bans across all Schengen member states.