Building blocks for a toy building set

A building block for a toy building set, the building block being releasably joinable to another building block, the building block comprising:

• a hollow main body comprising:
• a lower surface for supporting the hollow main body;
• an upper surface opposite to the lower surface;
• a plurality of walls connected to the lower surface and the upper surface, each of the plurality of walls comprising:
• a first wall section disposed on a second wall section, the first wall section comprising a first wall surface, wherein the first wall section protrudes from the second wall section;
• and
• the second wall section connected to the first wall section, the upper surface, and the lower surface, the second wall section comprising a second wall surface parallel to and distant from the first wall surface;
• spaced apart projections extending from the upper surface of the hollow main body in a direction opposite to the lower surface;
• spaced apart recess sections disposed within the hollow main body about the lower surface, each one of the spaced apart recess sections configured to enclose a second spaced apart projection of a second building block, wherein a longitudinal groove is provided between the side of the upper surface and a side of the first wall section, wherein the side of the upper surface is connected to the second wall section, wherein the side of the first wall section is a side close to the upper surface;
• spaced apart recess sections disposed within the hollow main body about the lower surface, each one of the spaced apart recess sections configured to enclose a second spaced apart projection of a second building block, wherein a longitudinal groove is provided between the side of the upper surface and a side of the first wall section, wherein the side of the upper surface is connected to the second wall section, wherein the side of the first wall section is a side close to the upper surface;
• an inner wall within the hollow main body, extending from the lower surface towards the upper surface, the inner wall connected to two of the plurality of walls at a right angle, wherein the inner wall and the plurality of walls forms the spaced apart recess sections;
• and
• inner longitudinal protrusions extending from the lower surface towards the upper surface, wherein a first inner longitudinal protrusion of the inner longitudinal protrusions protrudes from a first wall inner surface of the plurality of wall inner surfaces, wherein a second inner longitudinal protrusion of the inner longitudinal protrusions protrudes from a first inner wall surface of the inner wall.