custom_block.routing.yml

custom_block_menu in drupal/core/modules/block/custom_block/custom_block.module

Implements hook_menu().

custom_block_type_list:
  pattern: '/admin/structure/custom-blocks'
  defaults:
    _content: '\Drupal\Core\Entity\Controller\EntityListController::listing'
    entity_type: 'custom_block_type'
  requirements:
    _permission: 'administer blocks'

custom_block_add_page:
  pattern: block/add
  defaults:
    _content: 'Drupal\custom_block\Controller\CustomBlockController::add'
  requirements:
    _permission: 'administer blocks'