Rotterdam - Places of pilgrimage - 4

I'm building a mental map of meaningful places in Rotterdam. There is one rule: I have to remember the place myself. I cannot use my photo archive and I cannot use books. It has to be personal. The previous parts are here: part 1, part 2, part 3. The complete map can be browsed here: Google maps.

67. The blue spheres, Hilestraat - A collection of seven strikingly blue spheres in the playground.
68. Woman in burka, Hillelaan - Here I saw a woman in black burka pushing a black pram on two different dates. Was it always the same woman? A black madonna. Or a modern ghost.
69. Lonely garbage bag, Hillelaan - Each time I come here there's a lonely gray garbage bag sitting in an empty shop. The emptiness and loneliness are overwhelming.
70. Dirt triangle, Brede Hilledijk - Ancient dirt collects in a triangular (alluvial) fan shape on the concrete stairs. The rain sorts the garbage by size. Instant archaeology.
71. The portal, Maashaven - A spray-painted black portal by Influenza. There are several of them in Rotterdam and they are all connected.
72. Metro platform view, Maashaven - From here you have a great view of the nicely depressing industrial walls of the Maashaven Silo. There's a small illegal patch of grass growing between the concrete slabs.
73. The out-of-place plastic seagull, Maashaven - Someone has glued a small plastic seagull on top of one electricity pylon of the streetcar. You can only see it from the metro platform. It looks like an artwork, but could be a practical joke. I have not found any information about it.
74. The spooky birch trees, Zuiderpark - A grove of spooky white birch trees with a menhir in their midst. Birch trees are associated with amanita mushrooms and are thought to be magical in Northern cultures.
75. Menhir, Zuiderpark - Several modern, artificial menhirs have been placed in the park.
76. Dead poplar trunks, Zuiderpark - The grey trunks of dead poplar trees are like ghost sticking out from the neglected greenery.
77. Geometric constructions, Zuiderpark - Beautiful but disorienting constructivist artworks. On the border between art and functionality. Difficult to interpret. They are not on any list of Rotterdam statues.
78. The apple trees, Zuidplein - Next to gloomy concrete stairs, going from a boring sidewalk to an equally boring internal courtyard a (wild?) apple tree grows. It bears fruit but still unripe when I was there.
79. The roof cross, Wevershoekstraat - Some ornament has fallen from the roof of this 19th century house, leaving only a cross shaped frame.
80. The falling rider, Mijnsheerenlaan - A monument for 40 men executed during the German occupation of the Netherlands on March 12, 1945. By Marino Marini and Maarten Struys.
81. The poplar above the rooftops, Zuidplein - From the platform of the metro station you can see (in the summertime) one dark menacing poplar looking at you above the rooftops. An enigmatic, silent personality.
82. The poplar mountains, Zuiderpark - In the summer the dark mass of poplar trees looks like a mountain range. Imaginary mountains, trees and clouds, are the only ones we have.